You need to work out why the wall is wet, otherwise the mould will keep coming back regardless of how much you treat it. Using products on the mould just treats a symptom but the underlying dampness will still be there so the mould will come back, and the dampness starts a vicious circle because it makes the wall colder anyway.
Whereabouts on the wall is it? Is it an external wall? Which direction does it face? How old is the house? It could either be due to a leak on the outside - so have a look and see if there is a leaking gutter, large crack, missing tiles/slates etc which could indicate this, or it could be condensation.
Condensation is caused by an imbalance in one or more of four things: amount of moisture (does the house produce excess moisture, for instance by drying clothes on radiators in rooms, bathroom not having an extract fan or not using the window to let moisture out); lack of ventilation (i.e. the normal amount of moisture can't get out); inadequate heating (means that the air can't hold as much moisture and it therefore condenses out on the coldest surfaces), and/or inadequate insulation (often forms on the coldest, north facing outside wall, where the air can't hold the moisture when it hits that cold wall).
So you really need to have a think about why it is happening and try and work out which of those four factors you need to change in order to prevent it from recurring. Why is your room so cold? Does it not have heating or do you not have it on? Is it north facing? Is there a lack of wall/loft insulation in there? Do you dry clothes in there? Is there an extract or window in the bathroom? etc etc...
If you paint over it/use a mildew remover, it might stop the mould (for a time anyway) but it won't resolve the damp that causes the mould. To resolve the problem you need to stop the reason that the dampness is happening.
Good luck xx