Unfairness

I once signed up for contract cellphone I think around year 2010, Telkom failed to load my Airtime and data for consecutive three months,I tried several times to raise attention with no luck and ended up reversing the previous billed amount I my bank.

From the fourth month till the end of our contract they served me well. I'm now trying to apply for contract cellphone again and they keep rejecting my application due to outstanding amount which was +-R850, today I went to the store trying to resolve the issue but was told the amount is now around R1400 and they can't refund what they owe me.

I would like Telkom to be fair and civilized, let's reach an agreement that suits us both because this situation was not of my cause in the first place and would like to know from when did +-R850 accumulate charges to R1 400.