Is this their "Gen 6" boards they slap in everything? When I was using 3DStuffMaker electronics I came to find out they actively remove the bootloader. This makes it MUCH harder to read and write the chips. I went and bought a USBTiny clone. (https://learn.adafruit.com/usbtinyisp) It will hook up to the boards header pins and gives a USB connection to your computer. It will let you read the firmware as it was compiled. This is only really worthwhile for backup. You won't be able to make changes to it.
I know you said their support is brushing you off. WELCOME TO THE CLUB! I hated every aspect of that company. Eventually, they did send me the config file they used so I could compile a new firmware with my edits. I still had to use the USBTiny to write the new firmware. I found out eventually I could have written a bootloader to the board and made it normal again. I had everything setup to use the USBTiny and was content for awhile.
Ultimately, it was a relief when I ditched their Gen 6 electronics and swapped to a Geetech Printrboard. It adds a fan, 2nd heater, and SD card. Maybe these are already available on yours, though? It was a really easy swap since I had already figured out the firmware BS.
