Citibank Credit Card Complaint

Citibank Credit card department,

Sale of account Maryland

I had a Best Buy card from -/-/-, that was owned by - - with debt protection at the time, always paid it no problem, until -/-/-, when I had a back injury and started receiving - and filed the debt insurance claim. No problems, Best Buy accepted my claim. Now Best Buy sold their card to Citi Bank and I am being sued for the amount by - -, I guess owned by Citi Bank. Obviously an oversight on someone 's behalf, not mine. I paid the debt insurance filed the claim, and now am being sued. Please help