Cell C failed me

I signed up for their Cellphone device and a month later,I cancelled it but they still charged me for 2 months but their contract stated that if I cancel within 30 days,they will refund me all the premiums paid,but sadly that didnt happened and there was no explanation on how I was charged for 2 full months after cancelation,the only explanation that I received was,You have to pay or else we will block your account,then I made arrangements to pay ,they then blocked my account which I thought it was suspicious because I had already agreed to pay the money they were supposed to refund me. The only thing thety had to do was to explain to me why they wont refund me my 2 months premium coz I cancelled in a month and they charged me for 2 months