Getting billed for outgoing calls on distinctive ring number

For the past few months I've been getting charged for a few calls each month made from my incoming-only distinctive ring number. A couple of times I've been credited for them but last month my request for credit was ignored (there were two calls listed) and this month there's another new call. Billing and Tech support always initially claim these are legitimate but when pressed on it I was (until last month) getting credited back. They don't see a problem with an outgoing call being billed against a phone number that has no way of calling out. Has anyone else seen this? If you have a distinctive ring added to your phone line, check your bill! The extra charges will probably not be noticeable if you don't check the line item charges.