Suppose to be top up

Good morning.<br> I have 4 contracts at MTN, I have been a client of MTN for around 10 years now and in all this time I always take top up contracts because I dont want to get an unexpected surprise at the end of the month. My installment on my contracts are usually around R 2000 and I budget for it as such. At the beginning of this month I was debited R 7500, So I knew that at the time MTN had some labour issues with regards to strikes so I thought this must be a mistake. I then went to the bank, reversed the debit order and paid R 2000 as I am use to paying. I received a SMS on saturday stating that I ow R 6500 and MTN would suspend my contract, so I went to the store and found out that my Ipad contract was a open contract after I requested it to be a top up, because my children play with the device, I dont know what to to, the truth is I can not afford to just pay this amount and I do not have a leg to stand on because I trusted that this was a top up contract when I upgraded this contract. This is unacceptable from a service provider please assist me I dont even remember the consultants name at saveways MTN that upgraded my contract. I upgraded about 1 year ago