Wendy I am billing with ibill and CCBill and not registered in the US.
YOu only use the convenience of the rebill. You still have the advantage of the contact email over your competition. So contact them explain the stuff and ask them to sign up again using either your new biller or another payment method. If your site sucks you have a problem but if not you get to keep most of them.
Do something like 50% off the first month you resubscribe and you will just loose some money you keep your customer. That's business it requires some work every now and then
