S.C.
1. Start by contacting the folks at CCCS. If you completed your paperwork correctly, you listed the childcare amount in there and that will be taking into consideration.
2. In order for him to "legally" change the visitation he'd have to go through the courts. This means he'd have to serve you with the proper paperwork and both of you would have to attend the hearing for the modification. If you do not appear in court then he could very well get his way. If you appear in court you'll have a say in the matter. If you don't have a court ordered visitation schedule and custody ruling, you may want to beat him to the punch and file for one.
3. Hang in there. September will be here soon. Most men throw threats just to get you to back off. They have no intention of filing court papers and appearing in court. Most of them are afraid of the law. LOL. Try not to stress over it. You were married to him so you should know him well. Consider if he'll really do anything or if he's just blowing smoke?