The problem is that if there are issues with the statutory declaration, then the notice was invalid, and the PRTB will automatically find in their favour. You will then have to take a separate case to try and recover the damages. The problem is that they don't allow you to do the sensible thing of deducting what they owe you from what you owe them, and just pay the difference. You have to pay them in full, or you're in contempt, and then get hit with even bigger fines. That's why I suggest you get onto a solicitor to check whether the notice was valid.