You've got "StainGate".
If you don't know what that is, better start reading up on it.
Briefly, the MacBook Pro's have a VERY thin, sprayed-on anti-glare coating.
The coating is VERY fragile, and cannot withstand excessive "cleaning".
It will start to flake off, resulting in stains and "scratches" like you see on yours.
I believe Apple had a free screen replacement program for this, but not sure if it still is in effect.
I suggest you call Apple Support AGAIN.
This time, remind the person you speak to of "StainGate" (be sure to mention it as such), and that Apple had an extended warranty on the display.
See what they say.
IF they offer to send you a prepaid shipping carton and replace the display as "part of the program", DO NOT REFUSE. Send it in, and get it done.
And when you get the repaired MBP back, learn how to care for the anti-glare coated display.
You DO NOT want to "clean it" very often!