Theft by MTN on Transfer of account to another person. Random Pro Rata charge !

I go into a MTN branch to find out how i go about change the cell phone account from my mothers name into mine and change banking details so the debit order comes off my account.

The next statement I received from MTN is R605.00 more than my usual monthly payment. When I query the amount they state "Please note the invoice dated 2018-08-13 was for R1551.92 due to the customer swap charge of R150.00 (excl. VAT) as well as the subscription pro-rata of R375.81 (excl. VAT). "

Now I was aware of the transfer fee but nothing was ever communicated to me about a Pro Rata fee, when I questioned the Pro Rata fee the response I received said that due to the transfer they consider it a new account even through this contract expires in October when I would have had the contract from 2 years.

I would consider this to be pure theft! As I never received any communicate of this additional amount. Nor have they actually changed the bank details on the account.