Poor customer service.

My account was handed over Shapiro Shaik& Defries attorneys, an agent from there phoned and gave me a settlement amount which I paid. I even got a paid up letter on FASTA portal. Now I'm getting legal threats from LGR incorporated, also collecting for the very same loan. According to FASTA my account was handed over to LGR, so who gave my account to Shapiro Shaik? Who provided me with a paid up letter? And why must I pay after settling?