Tell them you want the firmware and eeprom as a last ditch effort to fix it, before you Skip for a refund / do a charge back.
If it's a one of a printer, I wouldn't install the official firmware for said printer. Odds are they're using a modified one to get around protections... This is also probably what's causing your printing issues. If the firmware has protection, and you install it on a clone.. odds are you'll brick the printer.
There's no reason for them to take 3 days to respond to you. They're likely just dicking you around, hoping you go away. Or if your within the return period/ charge back period, hoping the time lapses.
You have to be firm with these guys. Tell them you're not a beta tester, and expect it to be fixed by xx date, or a charge back will be initiated with all the emails / whatever as evidence it's not working, and they haven't been very helpful in fixing it.
Then follow through. Best case, your credit card company refunds you your payment. Sometimes they'll just eat the charge to keep you happy, other times they will do a charge back, which makes the company oay higher credit card fees... And shows them they cant spit out a product that doesn't work, with no support.
Buying Chinese is OK. Just buy one with a lot of reviews, from a trusted site. And even then... It's going to have 1/4 the support and reliability as a original one.
I'd buy one for fun, but not for production needs. Odds are when you need it the most, it'll be nothing but a
paper weight.