too-frequent but intermittment connection issues

I've been having intermittent connection issues for about two months, and it's gotten particularly bad in the past two weeks.

I'm fed up, and figure I must need a service call at this point. But what happens if it's working fine when they come? Can they still fix the problem if it's working when they arrive? Am I going to get charged every time they come out and it's working?

My modoem isn't outdated. I checked.

Thanks