At this point, I would put my focus on finding new friends. You are putting a lot of effort into maintaining these old friendships and it doesn't sound like they are reciprocating.

It could be that they are hurt you cut them off a few years ago and not willing to trust you? Or perhaps you have all drifted apart as you've gotten older? Friendships do change over time.

You don't have to cut them off, but I would try to accept that you are no longer as close as you were and move forward from there. Do you think talking to them directly would help?