Breach of contract with upgrade

I recently upgraded with Cell C and part of the upgrade was to receive 12GB free over a 4 month period (3GB per month) from 1 October 2015. I have it all confirmed in writing and have been requesting why this has not been done since the beginning of the month. I get ignored then responded to days later only to be told it has been escalated to another department. It is now the 20th, 3 weeks late, and I have still not received even 1 free KB, only to be told that it is still being \looked into". If I do not receive my free 12 GB's I will be cancelling this upgrade due to breach of contract!"""