RCS Finance Debt collectors.

I was convinced by an over eager RCS consultant at Builder Warehouse to sign up for a RCS Builer Warehouse Credit card. I realised that it is the worst possible interest rates and decided to cancel the card. I contacted RCS to close the account and they sent me the settlement amount which i paid immediately. Problem is i keep on getting cals from Debt collectors saying i owe RCS money with threats that i will be handed over to attorneys for payment.

How do i stop this ****mers from going away??