You should never gotten into this situation to begin with. Because you gave them free support it's going to be hard to break the habit. Good customers understand that your time is money. I would write them a letter stating that going forward they will be charged regular rates for your services, you will no longer be able to provide support for free. If they are as good as you think they will understand. If not, at least you will find out that they were only being good because you were giving them something for nothing.

-Hal


CALIFORNIA PROPOSITION 65 WARNING: Some comments made by me are known to the State of California to cause irreversible brain damage and serious mental disorders leading to confinement.