Once they have your contact details you will be pursued relentlessly to sign up with them.
In fact, YOU do the work for them in telling them what banks you have had accounts with or any credit agreements you have ever had. All they do is send a standard form off to these people and await their response, creaming off 25% or more if any cash comes back.
In my case, I know I have never had payment protection, but thought I'd see what they did. I refused to take part in their interrogation, telling them it was up to them to find out, which terminated the discussion. I received phone calls, texts and emails from them for ages until I threatened legal action for harassment.
Have nothing to do with them. Do the job yourself as advised.