Bad billing practice

I have had a mobile contract for R599 for many years, after the first 2 years I paid off the device and the amount was removed from the contract. So I've been paying R529.61 for the last couple years.

Recently, Telkom issued a statement saying they would increase these "R599" contracts by R20. So the resulting amount in my case should be R549.61, if you consider the device being paid up.

They are now billing me R619! Almost a 19% increase! Having called them their response is, "you can take another contract at R499", shortly after which I was just left on hold for 10mins.

I don't want another contract, making me bound to Telkom for another 2 years. I just want you to fix my bill, so I pay for the data only, OR send me another router if you're going to charge me for that.