Unexplained loss of airtime from my phone

On the evening Saturday18th September 2021 I loaded R60 airtime to my phone. Without making any call I went to sleep till morning of the 19th. On the morning of the 19th I made a call of 1 - 2 minutes. While on the call talking I heard 'Your airtime is finished and call is terminated' voice :(

That was the end of my R60 airtime, I let is slide. That afternoon I needed to make a call so I loaded R20 airtime to my phone. As I attempted to make a call a voice said 'You have insufficient airtime to make a call, please load airtime'

That was the end of my R20 airtime. Now I was not sure whether to load airtime or what so I called MTN customer service line.

The lady told me she is logging a ticket to investigate the matter and feedback will be in 8 - 72 working hours. I was sad that I could not make the call I needed to make so desperately but customer service cannot do anything to assist in getting the call done. It is my problem.

Late in the evening I loaded R15 using MTN yellow buck, once again the aitime disappeared out of my phone before I can put a finger to it.

Today the 23/09/2021 I did not get any feedback from MTN, so I call to hear what the investigation finding was, I was told airtime was used on data. I told the consultant that I have opted out on out of bundle rates and I have data available on my phone that cannot be the case, She checked and confirmed that I opted out in April already. She tells me she will log a ticket back to IT to investigate further.

I am still stuck with a phone that without airtime as I scared to lose more money in vain.

My problem with MTN: 1. No feedback provided 2. No interim solution while investigation goes on 3. Investigation done was not thoroughly done as there are loopholes not checked there meaning there is incompetence . 4. This happened earlier this year and I let slide because it was airtime bought with yellow bucks.