Terrible Customer Service

I renewed my Data contract with Vodacom Consultant and on the phone I was quoted R329 but invoices came as R349. I made more than 14 calls on different days from November 2017 to April 2018 with no joy. I now don't know how to deal with this issue because Vodacom Consultants told me the written quotation said R349 and after I requested Voice to be listened to, they confirmed that they heard Consultant Hilda agreeing with me at R329 but they work with what is written down so "Sorry Can't help". This is a terrible experience I ever had with Vodacom since I have been their client from 1998. Can anyone please advise what needs to be done in a case like this?