Vodafone GSM Tariffs Increased a Lot

I've been using Vodafone postpaid for the past 2.5 years. Lately, as my current Red 18 GB package's contract is about to end, I was given a renewal offer that costs almost three times more than what I'm currently paying. I want to continue my contract with a plan and pricing that's similar to what I've been using. If not, I'll have to change to a different service provider. It's really disappointing to see that new Vodafone customers and people getting new lines get better deals with affordable, high-data plans, while us loyal customers don't get any better options. I feel like they don't value me as a long-time customer, and it's really important for telecom companies to appreciate and keep their loyal customers. I hope Vodafone gives me a good deal when it's time to renew my contract, considering how long I've been with them.