Thanks for your post and welcome to our community.
I am really sorry to hear that you're having some issues with the services, this isn't good.
Is the Samsung A20 from us directly?
If the phone is advising that there is no SIM or SD card then it does sound like there has been some internal damage caused and the phone isn't registering them. This would also explain why calls would be dropping out when it does register a SIM is fitted.
You can have a look at our Phone Fix tool here for further diagnostics.