Mary J. Blige has now counter-sued the entertainment company that is suing her for allegedly defaulting on $145,000 loan in advance and refused to pay it back.

Vision Entertainment Worldwide sued the R&B singer for bailing on a concert she was supposed to perform back in December.

Seems like a pretty straightforward case, but not so fast, according to TMZ, Mary isn't returning the advance because the entertainment company broke the contract by trying to get her and her crew to fly coach.

Mary's response -- sue me ... sue you! In her countersuit, MJB says if anybody breached the contract ... it was VEW -- because it failed to provide first-class air travel for her and her crew ... because that's what an artist of her stature deserves.

Mary J. Blige is a well-known R&B legend in the world, but this isn't the 90's and she isn't as hot as she used to be. And then again, don't NOBODY want to fly coach these days! Yes I said it...