Heater blowing cold

[J1MMCD]

Posted a few months back about heaters not working but have more detail on it now and hoping someone has an idea or solution.

Car is a 2010 B6 highline estate. It has the 3 dial Aircon/heater control panel, if I set it to windscreen the heaters blow cold and the aircon button is lit. Turn the aircon off and it still blows cold air.
I’m also pretty sure my aircon isn’t working as it doesn’t seem to cool the car much, not sure if it needs regassed or has a leak but right now it’s not a priority.

On all other heater direction settings I get warm air as expected, if I get cold on any of those I rotate the dial to cold and back to hot and get hot air again.

I’m intending to flush the system and refill but it’s not an easy job to get into (for me anyway) so any hints or tips would be welcome.