if they have prepared ad submitted a defence, they have already incurred legal costs on your case.
I would think carfully about why they are only offering you the 540 and not the full ammount before you wait it out. If they have good reason not to refund you the 260 difference, you could lose the lot in court.
As in - to make myself clearer - if the 260 relates to charges for something that was lawful on their part, you risk losing the lot and paying the court costs to boot.
Banks are fighting back now cos its costing them millions, and most claims I have seen over £500 are being defended fully.