I had a similar thing happen to me in the early 2010's where my name was linked to someone else's that was very similar, who'd run up debts for water, electricity and mobile phones at an address hundreds of miles away and now they were chasing me for his debts. While people on here are right that you shouldn't completely ignore these letters, be prepared for the run-around from the debt collection agency if you do try to contact them, especially by phone.
They don't give a sh*t if you're the debtor or not - as soon as you speak to them (especially if by phone), they will take that as an opportunity to get you on the hook for anything they can, whether you agree to it or not. They'll ask you to do the impossible task of proving negatives, do things like send them photocopies of your passport to prove who you are (which you then have no idea what they're going to do with), etc. and then gaslight you whenever you try to challenge them saying they've never received any letters or phone calls from you even when they have, or even better just sell that debt onto a another company (probably a different arm of the same conglomerate) and then you have to start from scratch again.
Better to do the "not known at this address" trick and if you still do feel you have to correspond, do it in writing only stating certain facts and not responding to any other of their points. From recollection it is something like that you are not the person named, do not have any knowledge of this debt, and that FCA or OFT guidelines (* can't remember off the top of my head which one it was) state it is against the law to pursue third parties for debts not owed unless physical evidence of the original contract/invoice is provided (which of course they cannot do).
I ended up getting most of the above info from the following website:
https://legalbeagles.info/forums/fo...8-dealing-with-dca-s?7923-Dealing-with-DCA-s=. Now the thread on there is from 2008 and so is probably out of date (but search elsewhere on the site and you'll probably find much more recent/useful threads) but it did work for me - I'd been going back and forth with various debt collection companies for 6 months without getting anywhere, but as soon as I started sending out the template letter in post #4 on that forum, they began to cease trying to contact me or selling the debt on. Certainly worth a try.