Ten years of loyalty rewarded with bad service

I have been with Telkom mobile data for 10years now. I have never experience any problems in so far as thier billing until now. I pay a monthly subscription of R140.00. I missed a payment for March 1st and that attracted a penalty of an extra R202. How is this possible. What's worse is on the 23rd of March there was money in my account and they debited R390.00 and my contract as agreed was downgraded to R99.00. They failed to debit that amount even though there was money in my account and thus adding another R202.00 to my bill. As I speak, I owe R700.00 for an account of R99.00. this is madness and I will not allow this. If this is how Telkom rewards 10years of loyalty. I'm done.