ADT takes money *******ly and causes considerable hardship

After a burglary they installled 5 armed response systems in a property I have. Operations were great. I paid for the installation and tenants signed for monthly contract. Last month one tenant kept getting accounts for the installation. We sent them PoP and then now, at monthg end, they just deducted frull amount for installation. No permission to deduct more than the small monthly fee. Sales lady suposedly followed up but no response to me yet. Of all the tenants this one does not have the capacity to pay as they are struggling financially. Totally unsatisfactory. Need response immediately. This was in Kyalami