Vox refusing to admit they are wrong and disconnected my account

I joint vox last year where I took out the 90G day 90G night after the data only hold up for 2 and a half weeks we decided let’s upgrade to uncapped that will cost us almost R900 I emailed one of accounts manager mr D de villiers ,I ask him when we move over to uncapped will there be any extra fees added to our acc ,his reply was no , no extra cost will be added to your account the next month end we received a bill for R1300 we emailed him the bill and ask why our bill is so high after he told us over email that no extra amount will be added,he rep**** and said he will send it to someone in accounts to check for us and will get back to us which he never dis Tuesday we got home to our wifi being disconnected. We called accounts to ask what was going on we send them all the evidence we had off our conversation with Mr D de Villiers they just responded saying we can’t help you have to pay the full amount.