Upgraded contract but still billed incorrectly

I have received a statement for March 2023 for more than double the amount I normally pay. I called Cell C (084135) on the 7th March and spoke Azilwe to query the statement. Azilwe had advised that she was not able to access the statement and advised that she will get her Team leader to call me. I still have not received a call, I called back today (9th March) and on the voice prompts, I was advised that I was due for an upgrade. I went through to the Upgrade department and spoke to Rhulani who assisted with the upgrade but was advised to call back to log a query on my charge. I then spoke to Hlengiwe who explained that because I received the benefits for March, I will then be charged the ridiculous amount (R693 when my initial contract was R249) as I was not in contract (even though I just Upgraded). Hlengiwe has advised that she will ask her Team leader to give me a call which I doubt will happen as I was still waiting for a call from Azilwe's team leader from the 7th March. This message was forwarded to Cell C on the 9th March but of course I did not receive a call or a response. Please assist, surely there is a way to waiver the fee as I have upgraded my contract.