How do I remove my Hygena Cooker Hood / Extractor?

After many years my Hygena App 2102 extractor hood has stopped working so I have got a new one - a Hotpoint model. I have removed the power plug, taken out all the fixing screws I can see but the unit appears to be still fixed to the wall, just to the right of the duct hole, near to where the power cable comes out of the hood.
I can drop the front of the unit 50 mm and can see part of the white duct hole in the back through the top duct hole.
I gave a good wrench to make sure that it wasn't the grout holding it back and a lot of it has fallen out.
Looking at the inside there appears to be a band of masking tape vertically parallel to the back, around the brown plastic extractor unit.
I can see no way of twisting the hood off because of the cabinet above it. There is one small self tapper into the back wall and two into the cabinet above.
There appears to be no extraction ducting.
What do I do next?