This is one of the reasons why I claimed through an agent rather than doing it myself - all I had to send them was a copy of a bank or credit card statement showing that PPI was being charged. The company has dealt with all these awkward queries for me. If you really don't have the details (e.g. on past bank statements) all you can do is fill in what you can - but don't make any comment about being prepared to accept a settlement, leave that until they make you an offer, then you can decide whether to accept or not. If the offer's not good enough, you can then refer to the Ombudsman.