I sold my vehicle on 23 April

I sold my vehicle on 23 April. The dealership came to collect it on the 24th. I contacted Cartrack at 08:00 on the 24th requesting them to please remove the tracker asap. No joy as yet but instead I received at least 2 calls per day since then from the accounts department telling me my account is in arrears with R870 for the deinstalation!? I am telling them that I cannot owe for a service that was not rendered to me as yet! I contacted the Installations Dept again today. A very nice lady,Zinhle assisted me. She contacted the dealership to arrange for the removal of the tracker on 9 May. Once again the accounts department phoned me to tell me my account is in arrears and if I do not pay it,they will not remove the tracker! I do not have a problem to pay but why should I pay when the service wasn't even rendered yet? I am reinstalling it in my husband's vehicle and will pay when the removal was done!