Whats the right thing to do here? Should I just give up at this point?

you definitely have to make efforts to keep your friends especially now when a true friend seems to be much more harder to find. Unfortunately your friend seems to have forgotten this thing. I know from my personal experience how bad it can feel like when a friend ignores you or acts like a stranger when you call him without any explanation. I think that if you really want to atract his atention and make him realize that something isn't right you shouldn't call him on his birhday. Or you could as well call him on his birthday but be a little bit distant and then don't call him for a while and see what happens. Let him be the one that is ignored this time.