Did you sign anything from the PPI company? If you didn't then there is no contract with them. Don't be bullied by them, you can do this yourself.
I wouldn't accept anything from them, (your bank) but, download the PPI Questionnaire form, fill it in and send it off to them. They have to reply to you within 8 weeks and if you have some idea of what you are really owed and they don't agree then, you can contact the Financial Ombudsman direct and they will look at it for you.
You don't say who your bank is.
DON'T USE THE CLAIMS COMPANY. If I can help anymore, it'll be my pleasure.