Special offer cancelled when payment was late without warning

I took out a 3 month streaming package of R499 per month, last month. Without sending me a warning that payment is due, they disconnected me when it was past the next payment date which is unacceptable. Any company first send a warning before disconnecting you. Now they say there is now option to continue on the 3 month deal and that I am back on the full R800/month package which I can not afford.