Being punished for downgrading an expired contract

I have 3 contract lines with MTN and one of the contract entiltles me to 1000 anytime any network minutes charged @1.60 per minute .The minutes dont expire .My contract is due for renewal and i want to down grade to lower tarriff package .I currently have 4500minutes on my line which equates to R7200.00 which is money i have already paid MTN.<br> When i tried renewing my contract i was told i will loose my minutes and mtn will give me only R900.00 credit unless i continue on the same package which doesnt save my purpose anymore .All i want is to be credited with the right amount its not like they are doing a favor i paid for the minutes already.<br> Is this in compliance with the new credit act i wonder .