From everything you are describing, it sounds like you are having issues with connecting to Apple for any service. Check out the articles below to troubleshoot issues with connecting to the internet. The simplest thing to check for is to see if the date and time is set for automatic as that can be an issue for checking for updates or accessing the iTunes Store.
Thank you for your reply Norm.
Unfortunately, after following these steps my problem is still being unsolved. I restored my iPhone to the fabric settings via iTunes and it only solved a problem with checking for update. However, I still can't play any song or movie trailer. I'm suprised that even factory settings reset didn't help. Maybe it's a hardware issue? (but I don't think so tbh). Time and date is set up for automatic. Maybe it's a small problem but very annoying as I can't play anything. How can I solve it? Please help me, I would be grateful so much.
Thank you for your attention,
Due to the nature of your issue, you may find more information by using another one of Apple's support resources.