Airtime disappear and no concrete explanation given

So today on the 11 of November, I tried making a call only to find out that my airtime is depleted

Because I had not made any call since Yesterday evening , you can imagine my surprise when I was told that I had no airtime. I called your call centre and Sizwe Mngqibisa who was very helpful assisted me but here come the shocking part when I had to pull my itemized statement

My vodacom SIM card has been calling my Telkom SIM card for many minutes which has hardly happened ever. These two SIM card are in the same phone and there’s no way they call each other ever.

I don’t know how long this has been happening but it looks like it’s been going on for a while and I would personally like answers and solutions.

I know something fishy is happening because I have never removed any of those sim cards in the last 3 months from that phone so I am really struggling to find a reason why I would call a sim card that is in the same phone as the same SIM card and spend minutes on the line with it when technically, the phone does not allow that option at all.