I had the same situation, except that I am billed by MCI. When I inquired about the increase, I was told that a notice appeared in my last bill, but it must have been in the tiniest type, because I didn't see it.
Anyway, I said that I would rather cancel my service than pay the higher rate. They said, "OK, we have another plan that's 5 cents per minute 24 hours per day. The monthly fee is slightly higher than the regular plan." I switched to the 5-cent plan.
MCI is really a bizarre company. I have to call them nearly every month to get billing errors corrected, and they keep me on hold for 20-25 minutes each time. I think their system is set up to keep people on hold that long, in the hope that they will give up and go away! I don't do either; I stay on the line and get my small credits (usually $6-7, but sometimes a lot more) month after month.
JRF, you aren't cheap by my standards!
Bruce