Missing 30GB of Data in my monthly Allocation

I currently have a contract with MTN where I receive a monthly allocation of 120GB of data split between 60GB anytime and 60GB night express. This allocations happens on the 12th of each month, however on the 12th of December 2020 I received a different SMS which stated that I've only been credited with 90GB (30GB anytime and 60GB night express) as opposed to the usual 120GB. I immediately checked my balance on the App and it supported this statement. I called MTN on the 16th of December and spoke to a gentlemen by the name of Nhlanhla Mushwau who informed me that his system shows that I had indeed been credited with 120GB and must disregard the SMS that told me otherwise. He also told me to disregard the information in the app which supported my claim of having only been credited with 90GB. I found this very strange but insisted that MTN investigates the matter. He issued me with a reference number *** and told me that MTN's turn around time policy is 48hrs. On the 20th of December I called back to enquire about the status of my query. This time around I spoke to a gentlemen by the name of Sandile K**** who informed me that this matter has not been resolved even though it had been way more than 48hours since the matter was escalated. Sandile then told me he will escalate the matter again and he gave me a new reference number SMC/*** and told me about the 48hour turn around time as well. I decided to call again on the 22nd of December and this time I spoke to a lady by the name of Michelle Mkuzana and by this time it had been 6 days since the initial call I made to MTN to raise this issue but Michelle also told me that the matter still hasn't been resolved. Today is the 29th of December and I made another call to MTN and spoke to a lady by the name of Nonduduzo to whom I requested to speak to a supervisor/manager as the matter was still not resolved and no response had been forthcoming from the prior escalations made. Conveniently, no manager was available to take my call at the time as they were all on a Manager's call. I honestly do no understand this run around I’m getting from MTN and why they would breach the terms of a contract I have had with them for such a long time. It is such a disgrace to be treated like this as a paying customer. All I want to know why I suddenly started received a whole 30GB less data??