imessage

alright so someone blocked me as a joke but even after they blocked me, i could still get the messages they were sending, but mine weren’t delivering so i just couldn’t reply, and then i blocked them too to try and glitch it out or something, and then they unblocked me and i unblocked them too, i can reciever their messages, but i still csnt send any? i don’t know why, they unblockef me and i unblocked them, i can recieve their messages but i cant respond and it’s been hours, every one else i talk to works just fine except for this person, i’ve tried restarting, i’ve tried turning imessage off then restarting, ive tried the send sms thing, and nothing works, can anyone lend advice?