What is the wall sitting on? Your problem could be rising damp.
You could inject the wall (make holes about 9cm apart) with a damp proofing foam that fills up all nooks and crannies, smells disgusting and is administered by its own pump (same way as foam filling round windows)
Is the wall a downstairs one and is it NOT load bearing? if so, you could put a slate course in at floor level this would be impervious to moisture.
Could be done on load baring wall too but would need to be professionally done and could be very costly.
doesn't sound so nice .... Is there a fungal stop available that actually destroys the fungus at source rather than treating the mold? Mr Bricolage might be a source.
If the product you need is not available in Bulg, there's folk who drive over for the summer holidays who would surely help by bringing you what you need. Otherwise maybe online ordering and DHL?
Sure you'll get a load of advice from other folk, let us all know how you get on please!