Incorrect Billing

I was contacted by a Vodacom consultant to assist me with upgrading my Data contact from 20 gigs to 50 gigs, the lady informed me that I will be paying R249, now when I check they are billing me R272.99 which is way more than I agreed to, I even called them to complain about the billing but the lady I spoke to said to me I must ignore what I see on the app since it's not correct. This is ridiculous, hopefully someone will call me and tell me what's going on. I'm tired of Vodacom and it's tricks, this is what I have to go through every time I upgrade my contracts.