iMessage switched to SMS Instantly.

I was talking to someone last night and while talking my iMessages suddenly stopped and didn’t deliver for a bit then they turned green and SMS, last iMessage was at 1:29 and it was read then my next message became green at 1:33. Im not sure if the person blocked me or not. I called and it did ring and went through until it got disconnected but i don’t know if I’m blocked, it still shows SMS when i try to text that person. Can someone tell me something about it? They were getting sent and read and then just stopped. In the chat FaceTime icon doesn’t show up either. Sometimes I open the chat it says iMessage and when i close and open again it says SMS. Last time I was blocked, my message were blue and they got sent and were just on delivered and the other person never got them. And my call didn’t connect either. This time they became green and my call connected i haven’t called again but it rang.