Up to five million people across the UK could miss out on £100s having mistaken a legit 'fill this in to get your money back' form for junk mail.If you've had a debit or credit card since 2005 (so pretty much everyone), then please spend five minutes reading my Q&A below. It could be your most lucrative moment of 2014.What was CPP and how was it mis-sold?CPP is a worldwide company, which may've sold debit and credit card customers one or both of these products since 2005:Card protection products: These allowed customers to call one number to have all lost and stolen cards stopped and said it'd cover you for lost card fraud. These were commonly called things like Card Guard, Card Safe, Egg Emergency Cover and more.ID fraud protection: This promised to give you reports about your identity and cover you from the risk and liability of having your identity stolen.Both of these were systemically mis-sold and CPP was fined for doing so. Both CPP and the banks who sold it then "volunteered" to take part in a central collective redress scheme - basically a big pot of money to pay back mis-sold customers.How was CPP mis-sold?Banks put "activation" stickers on cards with a number to call to set up a card. But it used this as a ruse for CPP to sell you close-to-worthless card or ID fraud insurance,They were then told they needed £100,000 fraud protection cover; yet banks must cover fraud anyway, unless they can prove the customer was grossly negligent. In a nutshell, these major elements of the policy were virtually worthless.It doesn't stop there. Some people were told they couldn't cancel, the risk of ID fraud was overstated, it hiked prices without informing people, or auto-renewed with no opportunity to cancel.Have you binned a letter worth £100s?Seven million people who've had debit or credit cards since 2005 have been sent what are effectively "fill this in to get your money back" letters from CPP. Yet the last I heard (in June - there's been no update since), only 25% had sent them back.Many people have told me they binned them thinking it was PPI spam, but while the names are similar, this is nothing to do with PPI.Angela, for example, tweeted me saying: "Threw it away, then heard your advice and retrieved it, received over £200."Meanwhile, Caroline tweeted me saying: "Phoned up for replacement CPP forms, I did think they were junk mail when they arrived first time."But time is ticking - the forms need to be returned by 30 August, or as it currently stands, you won't get the money that was put aside to pay you.If you got a letter, just fill it in.No ifs, buts or shilly-shallying. If you got a letter, you had a policy and were probably mis-sold so fill it in and return it now - before the 30 August deadline.The bit people worry about completing is section B, so to help, see Martin's free CPP form-filling template statements - you can just cut and paste the one that fits your circumstances.Here's an example: "The policy said it'd cover me for up to £100,000 worth of unauthorised transactions if my card was lost or stolen. I didn't need this element of the product's cover because my bank/card issuer (delete as appropriate) is responsible for any transactions after my cards have been reported lost or stolen. "Lost your letter, binned it or didn't get one and should have?Act quickly and there's still time to sort it out - contact the scheme team on 08000 83 43 93, or go to the CPP website for the full contact details, and ask for a letter to be sent.People who've changed address since they had CPP may have had their letter sent to the wrong address.How much can you get?The longer you had the policy the more you get, and if you had both ID fraud and card protection you get more. You also get statutory interest of 8% a year on top.Some people do just get £20 or £30, but many get far more. Here are some of the emails I've received:Bernard says: "Got £45.82 back, not a fortune but good money for just filling in a form."Sheila says: "Just got £305 back from mistakenly sold CPP. I used your template which was great and the repayment arrived after only 4 weeks."Geoff says: "I was able to recover £250 from CPP. By using your suggested wording it worked a treat and got me a refund."