am I overreacting?

My friend likes to joke around a lot and sometimes they joke by blocking and unblocking me, but I don't really find it funny, am I overreacting or should I cut them off because to me it feels like a mindgame.

You're not overreacting by being upset about that at all. It's completely justified being ****ed off or hurt when they block/unblock you because you probably deem it as a more serious thing to do.
Dont cut them off before talking to them about this obvi. They prolly just think that it's a joke and doesn't have a deeper meaning than that so voice these thoughts to them and analyse their responses accordingly before doing anything drastic.

Definitely speak to them about it, because it can get confusing for you as to whether they are doing this deliberately or just as a joke. Also if you need to tell them something important, you won't be able to if they've blocked you and it makes you feel uncomfortable as if you've done something wrong.

It's not an overreaction - your friends are really weird for doing that. If they keep messing you around after you've tried communicating then do cut them off.