Dispute over payment

Good day, I have since cancelled my car track account with them around may and i was given an amount to pay after given a discount and i paid the amount that was given and they later passed credit as agreed, by the time credit was passed the account was already handed over to Nimble and I have been talking to Cartrack and Nimble for the past 2months and last communication with Car track i spoke to the supervisor who assured me that they will escalate the matter to Nimble to remove my account as it is settled and such never happened as i am still getting calls and messages from Nimble to say my account is overdue and when calling Car track again yesterday they said i should ask Nimble to remove my account yet they not providing me with Proof that the account is settled and closed.