Hello Everyone. Newbie Focus Owner Needing Advice On Fuse Box

Hi Everyone, am very new to this forum but hoping some of you may have some advice.

I own a 2006 FORD FOCUS LX AUTO 5 DOOR HATCHBACK. I bought it in May this year from a ford dealer in London. Ever since I bought it, the windscreen washer has not worked. When I first noticed this, I tried cleaning out the holes with a pin as I could hear the pump was still working but this didn't fix the problem. However as this was not a major thing, and I had an 8 week old baby to look after, I hadn't got round to doing anything about it.

I took it to the dealer the other day as the paperwork I had said it was due for an MOT. I mentioned the windscreen washer issue and they said they'd have a look at it for me while doing the MOT. 3 hours later, I am told that it is not in fact due for an MOT until March (that it was MOTd in April before I bought it from them - but I do not have any paperwork to prove this) but that they have discovered that the fault with the windscreen washer (which it will fail MOT on) is because of the fuse board/fuse box, which is burnt/melted and needs to be completely replaced. They did show me the box which was blackened and melted in one corner.

Does anyone know how much this should be to replace? I'm obviously hoping that they believe that they actually sold it to me like that, but obviously there is no way I can prove that this never worked (kicking myself for not going back straight away!!). Also, is there any way that they could tell from the amount of damage to the fuse box that it is an ongoing problem that couldn't have happened in a few months? Help!! Any advice much appreciated