Cartrack asking for payment for SERVICE NOT RENDERED. Manager Megan Dawood,doesn't return calls

CARTRACK's Call Centre Manager Megan Dawood refuses to return calls. I have been requested by Cartrack to pay for repairs to unit that THAY HAVE NOT REPAIRED. The call centre staff call every day requesting for payment-- I have repeatedly told them to provide proof and details of the unit that they repaired and NONE of them can provide that information and yet they are rrequesting for payment. i requested for the manegr to return my calls.. and she's obviously too busy to do so. Lindiwe from Cartrack even called early on a Sunday morning to tell me I am owing them R600