Vodacom missing roller over contract airtime

I have 5 contracts with Vodacom. I pat all most R1900 per month. I am a pensioner. My daugther uses the one contract and has bee overseas so she only uses this sim on the day she lies out or home. Then switches to her UK sim. He unused airtime is supposed to roll over. I queried why there was no roll over for 4 months. I was told the airtime had been used. I know for a fact in at least 2 of those months the sim had not even been in a device to use the airtime. When i requested proof on how it had supposedly be used I was told I needed to pay R17 per statement to get proof. I am shocked and appalled that this is happening. These cell companies already take advantage with their rates now they don't even uphold there policy of airtime roll over of unused airtime on contract. I feel like they are taking advantage of the aged and those that are not technologically savy. Some airtime was used to purchase 1 gig in one month to avoid losing it, but this definitely not the case for all 4 months. This unused airtime should be credited, otherwise I have paid for airtime that was never used? Surely I am entitled to have Vodacom explain how it was used if I did not use it and not have to pay more for the privilege. Very disappointed