This gets a little messy, but hang in there. It could be because MDC doesn't see your device as a Professional for some reason.
On your GO Professional 620:
Settings > System > About
Look for the
already installed map name/version and the serial number information.
Please report what you see.
The serial-number prefix for a GO PROFESSIONAL 620 is
ZE.
Then, on your computer, one more time:
- Open MyDrive Connect.
- Log into the same TomTom account associated with the device.
- Connect the 620 directly by USB.
- Wait for it to be recognized.
- Select My Content / View Updates.
- Look under My Maps. What do you see there?