Pathetic customer service

I received this statement for the month of November stating that I owe a pro-rated amount for promotional data that should have ended when my contract ended on the 17th November 2020,

I went into the mtn branch at Campus Square the 15th of November to upgrade and was advised to wait for the black Friday deals which I did and upgraded the 20th, which to my surprise checked my statement and found that I am going to be debited nearly R3000.00 for promotional data received on my previous contract that has been provisioned according to customer service.

How has the promotional data not stopped when the contract ended? Why don't you tell your customers the consequences of not cancelling or upgrading on time. Pathetic customer service!