Installation that never worked.

Good day

I have requested Netstar to install a tracker on my mom's car, but the tracker never worked. I informed Netstar and i was promised that a technician will be sent which it never happened. Then an email was sent that i must pay R770, the account will be closed. After paying i started receiving calls from a company that workers with Netstar demanding more money. It means i must pay for a service that i have never received on top of what was deducted and paid.