Hi there, the clause which says your employer can recover the payment in the event you make a claim against them is not going to be legally binding unless your employment was terminated under a settlement agreement. This is where you have to go and get formal legal advice about the agreement you a signing and be happy to accept the terms following such advice. If the employer simply puts this in a letter to you, without it having been included in a formal settlement agreement, it will not be binding because it basically prevents you from making a claim against them and you cannot five up these rights in any other way apart from under a settlement agreement.
In terms of changing the final figure if your salary changes in the meantime, you have to consider how likely that is. For example, does your contract allow the employer to change your contractual pay? If not, then changing it without your consent will be a breach of contract and they cannot just make such changes at short notice just before you are due to leave just to reduce your entitlement.
Finally, if you have the right to appeal the redundancy within 5 days but received the letter several days after it was dated, the employer should at least count the start of these 5 days as the date on which you received the letter.
This is your basic legal position. I have more detailed advice for you in terms of the options you have to pursue your redundancy pay if they decide not to pay you, which I wish to discuss so please take a second to leave a positive rating for the service so far (by selecting 3, 4 or 5 stars) and I can continue with that and answer any further questions you may have. Don’t worry, there is no extra cost and leaving a rating will not close the question and we can continue this discussion. Thank you