Why won't my iMessages deliver to one person only?

So for some reason my iMessages won't send to one person only. It won't even say "not delivered" I know I'm not blocked because when you block someone on iPhone your messages will say delivered but the recipient will never get the text.
Anyways this is happening to one person only, and the weird thing is she can text/call ME but I can't call/text her. All my other messages will send just fine to everybody else and I call anyone else as well. She's not having this problem with anyone else trying to text her either… I've tried turning my iMessage on and off but it's still not working. Any suggestions? I would really appreciate any assistance I can get, as I'm getting reasonably upset especially because something serious is going on between the two us and I really need to talk to her…

Do Apple Certified Re-sellers sell real apple products?

I'm from Puerto Rico and even being part of the US we have no official Apple Store. But we do have a store in our malls that claim to be "Apple Certified Re-sellers". The products I have bought there so far have been only accessories, example: iPhone cases, watch bands, etc. So other than packaging and YouTube videos I'm not really sure how to tell if the products are fake or not. Are they? If they are how do they get away with claiming that they are Apple Certified?

Old iPhone & new iPhone question?

I got a new iPhone for Christmas. I just transferred my info over from the old iPhone. Can the old iPhone still be used for calls and texts using the same phone #? It would be handy to give to the kids as an emergency phone without having to add another line to the bill.

PURCHASED MUSIC DISAPPEARS WHEN I CLICK ON IT?

I have an iPhone 7 and click on music in my library that I bought on iTunes in the past, when I do it disappears completely (when I look on iTunes to see if my phone still recognizes that I own the song it says the price like it was never purchased). Other times I click on a song it says "this title can't be played right now" and turns a light gray but still shows up in my library. How can I fix this?

Imessage not working, not delivering and turning green with certain number?

So recently i went to bed and when i woke up I could no longer text this specific person. I thought they blocked me so i deleted the convo. I got an email from them asking i blocked them? I tried texting the messages turned green when she has an iphone and it wouldn't deliver. Hers wouldnt either. I've signed in and out of imessage but nothing worked so far. What's wrong with my phone?