Sudden Installment increase complaint not handled

I laid a complaint regarding sudden change/increase of instalment. I have to date requested formal communication from the bank detailing the issues and the way they havery reached their revised calculated instalment. It seems the bank is unable to write to me formaly to explain the issue and the resolution of it. I keep getting the same response which is forcing me to make arrangements for the payment of the current revised higher instalment or increase my term. How is all this my fault or problem? And why are they unable to pit it on a formal letter on a letterhead? I cannot be expected to pay that much (+- R7k )for a property which was R595k when I took out the home loan. Without any formal explanation.

I keep receiving smses stating I haven't paid my installment whilst I have paid what was agreed. Until I get formal communication I will continue to do so.

Someone messed up and I must carry they ***** up financially.