Credit One sold debt that has been paid already to LVNV/Resurgent !

I have received a call saying LVNV owns some debt BUT Resurgent seems to be some sort of middleman for them.

I explained it was paid. The person on the phone put me on hold forever and I hung up. I received two letters from Resurgent claiming I owe about $700.

I called Credit One and the customer service agent with a very thick accent said I would receive a letter within 10 days. The letter simply says "notice of sale of your credit card account".

I have the email from Credit One offering me a balance reduction. If I paid 50% of the balance, they would waive the remainder of the balance. I paid online and received a confirmation email.

I live in Los Angeles, CA. I figured it is better to send a letter to both LVNV and Resurgent.

I don't think debt validation is necessary because the debt does not exist. I want to dispute the debt by sending the screenshots of the balance reduction offer and proof of payment.

Can I report Credit One for selling a debt that doesn't exist? Or this kind of mistake happens often?