Cartrack - use another tracker company

Just as our tracker fell out of warrentee, the GPS component started playing up, which is very convenient (not). We contacted Cartrack, if they sent someone out they would charge us R600. On this understanding we took the vehicle directly to them, we were not supp**** with a quote, so obviously we did not agree to a quoted amount, nor did we sign any documentation about costs or agreeing to pay any costs. Last night we got a sms demanding payment of R600 and that due to non payment we were not covered. After an hour on the phone this morning no a single member of their staff could assist us nor could they supply us with a contact number of the CEO as we are tired of getting the constant run around with Cartrack.