I paid my RCS account in December, and with it being the holidays, I accidently misplaced my proof of payment

I paid my RCS account in December, and with it being the holidays, I accidently misplaced my proof of payment. I have made contact with RCS and have explained what happened and even sent proof. They could have contacted the store where payment was made, but they never did. It is now 2 months, and they phone me constantly and write threatening emails. I find them to be so unhelpful, and talking to them doesn't help. I am just so frustrated with them.