Best guess is that if you had a price guarantee, it was that your plan price would not increase, but not that the taxes and fees on the service would not increase, which is why your bill is increasing. Which is total bullshit, I know.

Though the underlying issue is that the money is broken and that to maintain the same level of purchasing power they have to charge more units because each unit is worth a smaller and smaller amount of purchasing power.

I'm betting that if you measured your phone bill with the simple moving average of gold ounces it would decrease and I know that it would decrease if you measured it in Monero because my phone bill has done nothing but decrease over time