Very disappointed customer

I have upgraded my 20gig day and 20 gig night data last year to a 40gig day 40gig night. That was supposed to be R299. But I have been charged R455 since the upgrade. I have tried to resolve this issue since last year to no avail.Also they claim I use the 80 gig data and cut me of yet the data counter on the modem says only 40+ % used ..the network lately is very poor and the internet is extremely slow. Very disappointed as I have been a loyal customer for years and have 3 contracts.