I would presume you have asked Cayin support for help?
The reason this unit went out of production quickly is that they made the unit based on availability of screens (I recall 30,000 were at distributors). But then a cell phone company bought out the whole lot for a low end model. So the screens were no longer available to Cayin for manufacturing or support. They had stocked a limited supply or screens for support fixes but possibly that is gone now.
The whole thing is a shame because the unit sounded good. If it stayed on the market, then software support would have cleaned up existing bugs (particularly in the USB input / output system).
I don't use a traditional DAP all that much, but when I do I use this unit so I understand your desire to get it fixed. One possibility is to place a want ad on our forums; somebody might sell you their unit cheap. You could maybe create a Frankenstein of the best parts of each.