Oh dear GiloKez! I'm sorry you had problems.
I've only ever had one problem with it and it was when I didn't have any yoghurt and used milk with a squirt of vinegar instead. The texture on the outside was a bit rubbery, but still edible and tasted good. It's not a banana
bread style as the crumb on this one is very fine and quite light, but moist at the same time.
I only wonder if maybe it was the particular yoghurt and a combination of the oven temperature/time in oven?
I've found that thick, pot set yoghurt (or even sour cream) is best. Hope this helps