You have insufficient airtime to make this call but you know you have airtime, ask why?

On the 18th November 2018 I had airtime balance of R8.00 on my vodacom prepaid account when making a call on Wednesday the 23rd I discovered my balance was on 0.00 balance immediately I called customer service to query my balance at first they told me about the active contents that my be the cause for my airtime loss but my phone is an old model it was not possible I explained. Tebogo checked their system he then said to me there is a number starting with 072 095 he couldn't see the last 4 digits that I called on the 21 November that was when my airtime was used up. I told him I never dialed any number like that he then promised to investigate and to call me back the next day. 2 hours later I got a misses call from the mystery number Tebogo told me about the I then got curios I bought airtime to call the number only to discover that it was my voicemail box( using up my airtime). There and then I called Vodacom customer care centre to explain what the problem was but Trevor ( Agent) did not listen to me instead he said to me "there is nothing he can do I must do whatever I wanted" because their system shows the number 072 095 insisted I dialed, he was rude and unprofessional I ended up hanging up the call. The matter was resolved by Tebogo he called me back on Saturday the 23rd as he promised I explained to him the reason for airtime lost he escalated the matter to their technical team for investigation , I got a reference number before end of the call and I also received my airtime back the on Sunday the 25th November 2018, Thanks to Tebogo and his good listening s****s as for Trevor he needs to attend customer care and listening s****s training. I was hoping someone would call me to explain what happened but no one called instead I got an SMS to say we apologize for billing you incorrectly and that we have credited your account ,which does not make up for the inconvenience caused if the matter will still continues. but we live in South Africa where you either join them if you can't beat them.