***** on my vodacom contract

About a week ago my son told me that there's a "cross" on the top right of his tablet. On closer look I thought it was a network problem, that there was no signal. I called Vodacom to enquire about the problem, the consultant then told me that the number is blocked cause I have exceeded the limit. Confused, I tried to explain to him that when I signed the initial contract I agreed to pay only R118 for 24 months, nothing more nothing less and that the package is only for data. Then he proceeded to say "but ma'am when you upgraded to an iPhone last month...I interrupted him on that note and told him I haven't upgraded my package. Apparently someone upgraded to an iPhone at a vodacom shop in tygavalley in Cape Town, did a sim swap and exceeded the limit on the contract. I was given an email address to send my complaint last Monday, 11 Dec 2017, but it's been a week and I haven't heard anything from the service provider. On Saturday my accounted was debited with R872 but I was able to reverse it. I really don't know what is the way forward. I'm really disappointed at Vodacom.