Because to them, it the best part of 25% extra to be paid back on top of what they agreed to. If I were them, and reading above, I see your back against the wall with regard to repayments. You haven't got it and they know it, So who ever is to sanctions the extra repayment, will be putting their head above the parapet, if there is any hiccup in repaying this extra loan, and nobody is willing to to that these days, as its much easier to say no, and not be held accountable, even if it costs the bank more in the long run.
I would be more inclined to borrow the extra €4k from a family member and continue on with your plans.