Sudden Data Plan Price Increase at Vodafone

For many years, my entire family and I have been customers of Vodafone. I started using their services myself. My plan costs 33 TL each month, and I still have one week left before the billing cycle is reset. However, all of a sudden, I found out that they had increased the price of my plan to 136 TL! How in the world are they able to blindside me with such a massive increase in price out of nowhere? This is ridiculous on so many levels. In the event that this issue is not resolved as soon as possible, I will be forced to switch providers. Is this behavior even allowed by the law?