Constant calling despite Do Not Call and repeated request

They are actually up to calling me a couple of times a day. I press one and request them not to call again and they hang up...I started just stringing them on with a goal to keep their phone line tied up for at least 3 to 5 minutes. I figure that if they continue to waste my time I can waste their but it is really annoying. This morning I got a call at 4:00 AM...seriously!