Apps freezing on iPhone 6

I few weeks ago I contacted Apple via Twitter (@AppleSupport), explaining my issue. My issue is this: Since I updated to iOS12, all my apps freeze. Not all at once. And not the same apps every time. I have to restart my phone, then I can use the app again. When I don't use my phone, and want to use it again after a while, whatever app I use will freeze again. So, I have to restart my phone again to use that app. The latest to this is that my phone will restart itself during the night, when I have my phone charging. I am using a iPhone 6.

@AppleSupport gave me a case number: ********** 30569.

They also gave me a support number: ***. When I call that number, and chooser the option of "iPhone", I get the message to contact my service provider, and the line is dropped. I went to the website that I was also referred to. When I choose the "iPhone" option, I get a screen saying "We're sorry. We are unable to complete your request at this time. Please try again or come back later". I tried a few times, and got the same message every time. I would have at least expected to get an option, somewhere, to input the case number.

I can only conclude that Apple support here in South Africa are not really able or willing to help me. I left Samsung because their phones became useless and because I liked Apple. I do not think I like Apple very much any more