IPhone not sending iMessage to one person?

So I put a friend of mine on do not disturb for a day or two to keep myself from texting them. I took it off and texting was fine. I just realized that a lot of the imessages I've sent him (since Sunday) didn't deliver and they did not automatically switch to text. Why is that happening? I don't believe he would block me he s my best friend. But it is possible.

Is using my iphone good enough to film youtube videos?

So i've started my youtube channel this year in late February, and so far i have about 5 subscribers and over 100 views, and i use the back of my iphone 5C to film with the lock on, i feel like the qauilty of the camera inst that good so maybe that why people are not really subscribing? I don't really have the money to get one of those DSLC cameras right now, is there a camera that i can use that is cheap enough for me to buy at the moment that i can use to film with? Maybe with a view finder, or is there something i can do in the settings of my iphone that can make the videos come out more clearer?

It only uses up GB if you have cellular data on?

I have an iPhone 6s and I have data on my phone. And I have my Cellular data turned off but I keep getting texts saying I'm using to much GB? What am I doing wrong to make me use it up? Please help. I keep getting yelled at because of it.

Apps to download songs/music videos?

So I bought an iPhone 6plus but I'm unable to find an app that can download the songs. Apps like Spotify, iTube etc won't let me to download them when I go to the AppStore, it says that I must change my country (I'm not sure) then when I try to do that it asks me to pay or something, so please can anyone tell me free apps to download songs and if possible music videos also.