horrible experiance

what a horrible experience i am having with this creditor. I am now listed on credit bureaus for a paid up account.no matter how i try to reach out for assistance to be cleared, they ignore me and keep telling me they are escalating but nothing happens. Nimble group the third party calls me everyday to make payment arrangements for an account I've already settled. i do not know perhaps i am expected to pay both payjustnow and nimble separately for the same account......so helpless any advice