CLI Letter - Threatening Doorstep visit on Scandinavian debt almost sb'd

Hi! I received a couple of emails from CLI chasing what I believe is a creditcard debt (but it dosent really say). I ignored them, and now I have received a threat letter from them a bout doorstep collection. Now I know I could probably just continue to ignore them, but I rather not let them turn up as it would be embarrassing for my wife. Is it advised that I email them, telling them that I do not recognize this debt and it's up to them to prove it? (the post just arrived and it

So the debt is most likely credit card, although they are just referring to another debt collector in a Scandinavian country they are collecting on behalf of. (Intrum Capital). I moved nearly 10 years ago , and have not paid anything or dealt with any of then in that time. I know the creditors can "renew" the statue barred status in the country every 10 years , but I'm not sure they have done so. I believe (even though I'm not sure what debt they would be referring to) would be that old.