Who selected these windows? Who installed them? What do the old windows look like? What was the original plan? Everything should have been figured out before the windows were ordered and it looks like someone sold you an incomplete package- yay you have new windows plus an unfinished install. Looks like you need at least a sill and brick moulding but who knows if the window was measured properly to allow for that.

A lot of finger pointing between contractor who ordered the windows and the installer; we didn't feel like taking the matter to small claims court. Thx for the info

Who planned the project? Sounds like no one? Post photos of the existing windows and maybe we can help you find a solution. Obviously next time you need a better team. This is one thing I do in my business- bring together the installer and window supplier to the job and plan out the solution prior to ordering. We’ve had jobs we’ve measured three times to get it just right prior to ordering. It adds time and cost to get someone like me involved (architect, designer, etc) but would have prevented the finger pointing and probably cost less in the end.

Looks like a window was installed in an existing wood buck with zero flashing. If so, this is a disaster in the making.

Is the black remnants of the old trim- some quarter round and a sill?

You have stucco siding, you cannot just add trim without compromising your waterproofing plane. This needed to be dealt with on the front end, cutback back the stucco and detailed prior to installing the windows. And the windows needed to be ordered with the trim or at the least planned and installed with the windows and before stucco finishing. From the looks of what of have there, I would expect major water damage in fairly short order.

You have been screwed. Installing a window into rotted trim is not cool. If payment is yet due do not pay it .