There's a process you can do on your own. My friend who is a lawyer did it on his credit. There are sites that can help but basically you write them and ask for proof of docs you originally signed and some other things they need to keep those bad debts up. He got most of them wiped off and he legit faulted as you did because they didn't take the time or couldn't produce the legally required docs. This was some years ago so maybe they have better record keeping? I'm pretty sure the credit repair people do the exact same thing for high fees.
Yeah, i looked in to one of those credit repair 'agencies', and it's a scam. Basically they say the will guarantee for your score to improve over time, with one caveat.... that is that the credit reference agencies don't change their algorhyms, oh yes and you can't make any more credit applications. Basically do nothing, and they say your score might get better, and if it does, they take the credit.
Well i know enough about credit cards, to get 9 of them with £14k credit, without ever having had a stable period of employment.
I keep a track on all of my scores, Transunion (Noddle), Clearscore (Equifax) and Moneysupermarket,com (Experian).
The fact that i have been steadily paying down my debts, from £14k a year ago, to £4k now, means that, even though i do have two defaults, i am still paying them off.
I think some, or lots, of people max out their cards, and then cut them up. Hoping that somehow the debts, will mysteriously disappear. Well it doesn't. And at least by paying off a little each month, it still shows responsibility.
We have to remember that these credit cards cater for a wide spectrum of customers. From the bat poo crazy, to the wealthy but stringent millionaires. And guess who the cards make the most money from? And it's not the stringent guys!
Basically that's what i have learnt from UK credit agencies anyhow. Good luck!