My bedroom started to get a problem with damp walls in the bottom corner of the wall running along the outside. It was not so bad at the beginning, when the black spots of mould appeared I bought some fungicidal mould spray that is supposed to protect and treat the affected area.
The mould went [...]

If you are suffering from condensation dampness the following questions will help you to remedy the problem.
Damp caused by condensation will crop up in the following places

Cold corners of the room
Behind furniture
Cold surfaces such as windows
Inside built-in wardrobes

You may ask; how can I avoid condensation?
Reduce moisture
When you are cooking shut the kitchen door and [...]