Hi ZX
Do I understand you correctly?
You were in deep arrears.
The bank told you to sell the three properties.
You , ZX, had a shortfall of €100k
Your mother paid this to the bank on your behalf.
The bank has admitted wrongdoing and has paid you, say, €300k.
If I understand it correctly, it's not complicated:
You owe your mother €100k.
Look at it like this. Let's say there was no guarantee in place.
You had a shortfall of €100k which you could not pay.
The bank would not have paid you €300k. They would have paid you €200k.
Brendan