hello and welcome to the community forum
I would imagine the CS asked you to run some tests - have you been able to identify any issue or at least narrow it down?
I guess you know that sending a phone for repair would de facto mean the factory reset and still that may be your best option now
if the issue is with charging, you might consider swapping the USB port, if with the display, checking all the connectors, etc.
You might find contacting a local Angel also a good idea