Matrix Vehicle tracking does not let you cancel a contract nor are they contactable

It is impossible to cancel your contract with Matrix. They dont answer the phone nor do they respond to emails. I have emailed every contact they have listed to cancel my vehicle tracking account since June this year. They absolutely do not respond. I am paying for a service for a vehicle I no longer own and cannot get them to contact me. I hate to think if your vehicle must go missing that they are actually contactable to locate it.