Car transmission

So my transmission was failing a months ago took its to a mechanic charged me 2k to replace the new parts inside couple of months later the transmission starts to slip out again I take it back it came with a warranty so he calls the guy were he bought the part from and the guy tells him that they have no more of those parts and will have to wait so I have been waiting for weeks text the mechanic and he tells me he’s been calling the guy to try to see if we can get the money back for the transmission and the guy says he only does only exchange or credit idk what to do I just want my car fix i really don’t want to pay another 2 grand