IPhone 8+ doesn't receive calls right away and problems with connecting to internet?

I have an iPhone 8+ and I've always had problems with sometimes not receiving calls for 1-2 days after someone called me. That's not often but it's happened, and texts sometimes don't appear for a couple hours after they were sent to me.

Also been having a problem the past 2 or 3 weeks with slow internet connection, or none at all. My data sometimes doesn't even work. But everybody else in my house has no problems.

What could be the deal? I've restarted the router, my phone, and no change.

Broke an iPhone screen, what is the best course of action to take?

I just cracked the screen on an iPhone 6s. The phone is under a year old so I'm not looking to replace the phone any time soon. I had to not bought the Apple Care so I do not have the benefits. It will cost me $149 to repair the screen but I'm wondering if it could be cheaper since my phone is under a year old. And would it be possible to trade in this broken phone for another iPhone 6s or iPhone 7 (not looking for newer models) for cheaper price?

Do not suggest that I repair it myself, I do not trust myself enough. And I also am not going to repair stores outside of Apple since it is risky.