Treating customers fairly

I received a call from Cellc recently to advise that my current contract has matured and my new billing will be increased by more than a R100 going forward. I was not made aware of this change and especially regarding a financial change. The lady that I was speaking to insisted that this is how contracts work and if I was not happy I must change my service provider or speak to their customer services. I tried to advise the lady if I can speak to a manager or anybody senior. She was very rude and said that I need to speak to customer service and I need to call them and sort my problem out with them and then dropped the call. Why is an organization like this treating loyal customers in this manner. The lady was very unhelpful and rude to say the least. I need help!