Complete Recovery Corp Emails Don't Stop

Hello,

I had cancelled my Xfinity service but lost an item for return. I contacted a customer support agent and was able to pay off any associated dues to the lost item in December. As far as I can tell, my account balance is $0. Complete Recovery Corporation continues to contact me, stating that I need to return my equipment. Again, I do not have the item, and have fully paid for its loss. 

When I try to contact anyone at CRC regarding this, my emails bounce and calls are terminated before ringing.

Can something be done about this? Is there a list that my account is on, that it can be taken off of?

I would like to stop receiving communication about something that has been finished for months. 

Thanks