Checking a RBS PPI compensation offer

Hi newbie here.

I've received 2 letters from RBS today making an offer for mis-sold PPI policies on old repaid loans.

How do I check the amount they are offering - I have no paperwork relating to these loans. Can I :-

1. Ask RBS to provide a breakdown of their calculation
2. Send in a Subject Access Request (or whatever they are called these days) to ask for all information on these 2 loans

Thanks for any help.