This sounds like a difficult situation to be in and our hearts are with you. We’re not licensed therapists, so we can only provide insight or tips on how to navigate this from our own experiences.
It’s great that you’ve sought out counselors to help you deal with your feelings and how to navigate this. It sounds like your son is setting a boundary of not wanting contact right now, and that can be very hard as a parent. It will take time and patience to repair the relationship but your son may also not want to repair it. There may also come a time when he does read your notes but that’s up to him.
This is not an uncommon situation for parents of LGBTQ+ children. We hope that in time your son reaches out and wants to talk. If he does, we recommend reiterating that you love and support him, and want to be there for him however he needs. Finding a local PFLAG chapter in your area may be helpful as you’ll find other parents of LGBTQ+ children at their meetings who may have been through this situation with their kids. You can find your local PFLAG chapter at pflag.org/find