Businesses are going to work on what makes sense financially. So what they will do is add you to a ticket. Then when they get enough incidents they will consider doing something about it. Your best bet is trying to get MS to do the legwork on fixing the issues. They might not be able to but they might at least be able to identify the incompatibility which would make it easier for the AV vendor to fix it.
As far as handling the refund I generally tend to rule in favor of the customer if I feel it's a reasonable request. I'd rather have a happy former customer who could eventually become one again in the future based on how well I treated him.