Taking what is not theirs

I recently migrated from topup contract to prepaid. The day before my migration I topped up airtime by supercharging. The next day (after migration) I tried to make a call and the voice prompt indicated I had no airtime. I queried with Cell-c and I was informed that all contract minutes, airtime and data was removed during the migration. I indicated that the minutes, airtime and data was as a result of the prepaid top-up. Cell-c indicated that they would log a dispute to redeem the airtime. This airtime was given back to me later the afternoon. However, cell-c refuses to give back the approx. 400mb data and 400+ minutes that resulted from my various super charges. These super charges are not linked to the contract and are as a result of prepaid purchases. Cell C advertises supercharge as a pre-paid benefit? In my first attempt to escalate this matter to a manager, I informed the staff that i will be in meetings during the day and could only answer the call before 8am. The manager called me during a meeting. I tried returning the call after the meeting concluded, unsuccessfully though. After 3 phone call attempts to reach a manager or supervisor, Cell c has still not called me!