vw/audi 2.0TFSI no warm air after coolant pump change or coolant flush, seized heater valve

We had an Audi a5 with a leaking coolant pump in for service. Changed the coolant pump with thermostat hosing and filled up the system with coolant, but couldn't bleed the heater radiator. No warm air came out of the vents. After hours of trying to bleed the system again and again we disconnected the in/out let coming inside the cabin and tried to push air through (used vcds to open up the heater valve), but it was blocked. After bypassing the heater valve we finally got hot air.
It's hard to believe that the valve got seized during the change of the coolant pump, which makes one think he messed up the replacement of pump or incorrectly bled the system. It's end of summer and people haven't been using the heater much so might not even realize there is an issue there as well. Also, when the coolant is drained for some time the valves and other parts of cooling system can develop issues.
original part number of the heater valve is 4H0121671D