i can pay this amount is a lot for me

I have a Contract with Vodacom. In march 2019 i got call from Vodacom offering a migration, to tell you the truth it was tempting and i agreed to the offer but 5 minutes later i called them and cancel the migration. In April i have received the package of migration and i called the to enquirer on why they went ahead with the migration even though i have called them and cancel, they apologized and said it is fine i can go ahead and use it but they wont charge me for that. Now in May i have received the invoice that amounts to R1686,50 and out of this amount R1250.00 is for the cancellation of migration. Normally i pay R228.00 that includes router of 5GB. I called them and enquirer and they said i must pay that amount because i have cancelled the offer and downgraded. I told the the amount is too much for me i cant afford and they insist that i must pay the amount. when i want to cancell the entire contract they said i must pay R1500 plus the R1686.50 that is in the invoive.