Nimble group wants me to pay an account that have been settled

I had a contract with Autopage cellular. Vodacom service provider took over the account. The contract was terminated in 2016. I went to Vodacom and received a statement for that account. I shows that the account have been settled. I have emailed them the statement. They are phoning me asking me when I would pay the account. They gave me an reference APV23724