Liable for ****** Data Sim Bill

My router data sim card was ****** out of my router on the 11 August which I didn't realise I only noticed the on the 12th of August when I wanted to go online I immediately suspended the sim card. Now I receive my bill, and the person who stole the sim made calls bought a lot of data and SMSs on the 11 August, Telkom says am still liable for the bill because they don't have proof .. am really saddened at this because the agent even says she is aware I did suspend my sim. is there a way this can be resolved as I can't afford to pay for that kind of amount.