Sue the buyer?

The buyer (an Indian) signed the contract for our house at the end of May, however, they used all kinds of reason reject to pay the second deposit, then finally after ONE AND HALF month (after attoney review and house inspection, no problem with house inspection), they sent us a copy of bank letter (even without title) said because the wife's credit, they could not get the loan.

We knew they were lying, and waste our time for the best selling time, we lost around $15k because this.

Our lawyer said $15K is too small for him to take this case (we had a really bad lawyer, BTW, could someone know how and where to complain a lawyer's work), we want to sue him by ourselves, (It has been a long story, not just the money, he made us so angry, he cheated us for the whole time)

Could someone has this experience share your knowledge here for this kind of case? Thanks a lot! We are in NJ.