Misrepresenting contract costs shortly before increases come into effect

I was called by Vodacom for an upgrade mid March. Package costs were discussed with me, and I agreed to proceed. A quotation confirming the agreed amounts was sent to me via email on 2 April.

I received an invoice for a higher amount. I queried this. Investigations were started. They were "sure" though that it would go off at the agreed amount, not the invoiced one. No feedback was received.

The higher amount went off, and the next statement indicted the higher amount as well. I queried this again. An investigator was appointed.

Today, several days later, I receive an SMS stating that the billing is correct and that the higher price is duie to price increases on 1 April

In terms of the T's and C's, at least 20 days notice would be given before a price increase. This was not done - in fact, I was quoted the lower price inside that 20 days window. Furthermore, the quotation was sent to me AFTER the supposed increase came into effect

Not only are these not in line with Vodacom's own terms and conditions, but how the heck do you quote someone q price that you know very well will not even apply to them, as the upgrade only came into effect on 1 Apil - and the increased amounts were already known to Vodacom - at the very least, this is extremely underhanded marketing which misrepresents known information and does not disclose known changes.

I am not satisfied with the answer provided (and the delays in providing it)