You're a long-term, high-usage customer and they're canceling your contract? Call them and complain, if you want to keep it. Let them know what the issue is and that you have otherwise been happy with your service and you would like to stay. See if they can get you an Airave (if that's what you want, it would solve your service issues)... I can't see them looking at your account and just throwing that out.

And they'll want to cancel accounts of people who roam too much because they have to pay the other network providers for roaming time used, and the same applies in the other direction.