I believe you can give notice to cancel at the 11th month point, so that the contract actually finishes on the day (+1 year) you originally got the contract.
As for call vs. letter, it depends on the exact billing provider so you'd have to call the CS line of your billing provider to find out exactly what's the procedure.
As for call vs. letter, it depends on the exact billing provider so you'd have to call the CS line of your billing provider to find out exactly what's the procedure.