More pics

"The overhang was uneven from one end of our cabinets to the other."

Uneven overhang is not always top fabricator/installer error. If the cabinets are installed out of square or out of plane to each other, the overhang of the top that is in plane will vary. It has to; it's math.

I run into your sink problem in my sink replacement business. I am forced to choose between mounting a self-facing apron sink flush to the cabinet on each end and have uneven overhang as you do or have an even overhang on each end and have a gap between the sink apron and the cabinet. This is because the edge of the countertop and the edge of the cabinets aren't parallel. Not my fault. You'd be surprised at how often we see this. I round the corners to fool your eye and call it good; no caulked sink aprons on my jobs.

These guys were terrible templaters. Looks like they cut things square instead of to the walls. Faking repairs with estone with that much movement is going to be problematic. Post your layout with dimensions including overhangs and we'll see if we can recut and scribe our way out of this one please.

We spent a good deal of money into our kitchen remodel and the company we hired to do this job have remained mute and unhelpful.
Is there anything we can do

Ya. Don't pay them. If you have paper work verifying what stone you chose and a template for it that you signed off on, make them, make it right.

Obviously the templating was poor. You are right to be insistent it is redone. Did they come to your home after cabinets were installed to laser template?
But my real question is you said you picked out and ordered a 2 cm slab. That is a 3cm slab, so do you have paperwork that specifies 2 cm? Seems like there was a big error right from the ordering of the slab

No fabrication template was provided to me and we requested multiple times. We were told the slab had been cut already. We found this to be so disturbing as they had measured twice - the first time there was an issue with a small extinction to one wall that needed fixed. They had provided the fabrication template at that time so why not with the 2nd??
Yes - invoice shows 2cm but that’s not what we received.
There’s a seam running along the edges that appear to be two pieces about 1 inch thick stacked together.

That is 2cm with a 4 cm mitered edge stack.

Most of the issues lie underneath the stone, rather than being with the stone itself. Your cabinet installation, framing and drywall work, and prep for counters was substandard.

Your cabinets are out of square.

Your walls are out of square.

A fixed length object cannot fit smoothly and evenly between 2 other fixed length objects without being shorter than the measurement between the 2 other fixed length objects. Especially if there are multiple things out of square.

A standard side splash or tiled backsplaah will conceal the out of square wall gap. Or, the wall itself can be floated out.

The out of square sink issue will remain, but can be disguised by radiusing the edge interface more.

Nothing in my house is square either, but my countertops fit in perfectly, because they didn’t just come out and hand measure

@verbo the cabinet installer never checked before template to ensure cabinets were level nor our sink. When the counter was installed they found our sink not level. (Shims were used) So wouldn’t those issues fall onto the cabinet company not doing their job?
I have a farmhouse sink that is now pulled out of the base lopsided to compensate for the unevenness around the sinks edges.
I realize our walls are not square. Why would the fabricator used a 4 cm mitered edge to begin with?

@rtpaige03 agreed 100%. That’s what the template is used for even when the walls are not perfectly square. I feel that the cabinet installers did not do their job well to ensure that the cabinets were 1) level and 2) squared. As with our sink, we found it to be not leveled at the time of installation

@rtpaige03, my coutertops are perfect also, even though some walls and not square and plumb. I think if someone is really good in what they do, they are able to do it even measuring by hand. That is what happend in my case.

"my countertops fit in perfectly, because they didn’t just come out and hand measure"

@rtpaige03 - nothing could be more out of square than my kitchen and its wonky walls. The fabricator did a fabulous job and everything fit perfectly. The seam is also perfect. But they did the old-fashioned hand measuring and templating. No laser or CNC machine. They have 25 years in the business and knew what they were doing.

I am saying this because a fabricator who does the "more modern" methods of templating can still get it wrong, especially with over-reliance on the machine rather than looking at what is being produced (how can the OP's fabricator not see the issues with that installation?). And a fabricator who does it the more "old-fashioned way" but is skilled and experienced can still get it right without reliance on a machine or software.

"Why would the fabricator used a 4 cm mitered edge to begin with?"

"There’s a seam running along the edges that appear to be two pieces about 1 inch thick stacked together."

You do not have a mitered edge. You have a 2cm top with a 2cm built-up edge. If you had a mitered edge, your seam line would be at the top, not at the middle. Miteres are used to continue the movement of the stone through the edge and are more expensive than stacked edges.

That is a beautiful quartz!