POOR SERVES

I recently lost my mobile device wtich was on a telkom mobile contract, went into the store to migrate to a new device, signed a contract to state that I will pay the remaining 15 months of the phone on my new contract, 5 months later I get charged a once of fee of more then R5000!! i did not sign for this and will not pay it, its been 23 days now and telkom mobile still cannot assit me, the bank office person who tried to help is incompetant and cannot reason