Well when I pay 10 dollars a month to keep my IP address static I expect that my IP will not change period. If they make a mistake and change it I expect them to get my IP address back or to be reimbursed the fees I payed to keep it from happening. I don't think that's unreasonable.
I think it is. If they no longer own the block of IPs that you were in, there's nothing they can do about it except give you a new IP. And that is an example of what could happen, it isn't necessarily what happened to you.
