billing enquiries

I am having challenges getting assistance with my Telkom account.

I recently discovered that my account for Sept 18 was R450,Oct 18 R650,Nov 18 R650 and Dec 18 R650.

I enquired from Telkom Clearwater mall on 09 January 2019, and was told to log onto the app and someone form billing will call me.

Went again on the 10 January 2019,and was told my cap was R500 +150 monthly billing fee.

My concern is for over 18 months of the contract I was billed R150.Who changed the terms and conditions of my contract.

I cant get answers, but being billed and money taken.

So frustrated can someone assist.