How to tell if your texts are being blocked on Samsung Galaxy S3?

I’ve been trying to text an iPhone user on my Samsung S3 for a week now but they literally haven’t responded to any of my messages.

I’m not really sure if they’re just flat out ignoring me and refusing to respond or they’ve blocked me. I realize they could just be super busy and haven’t gotten around to me yet.

I don’t receive any error messages when I send them. It appears to have been delivered like usual.
Is there a way to tell if they’re blocking me?