How can I tell if a person blocked me

I'm trying to figure out the same. I think the person keeps blocking me and then unblocking me because when I send text messages, weeks sometimes months pass and the iMessage won't show "delivered." Then the person unblocks me and messages me and I can message back no problem. That happened earlier today, and now my messages won't deliver again. I feel like that's me being blocked... but I don't know definite, "if your messages are not being delivered, then the person has blocked you." That's what I'm looking for.

The only way to know if someone has blocked your contact on their iOS device is to ask them. The person being blocked receives no feedback and has no way to determine the block or not.

Blocked you from what?

I don't believe there is any known way for you to tell besides asking them or being told by them.

There is no way to know for sure, but apparently if you call the other person and your iPhone rings only once and then you get redirected to Voicemail, there is a chance the other person blocked you.