It looks as though the International Global Intelligence people have traced your ex-wife to her last known address in the UK and unless they know which country she went to live in then it's going to be pretty hard finding her. I've had this happen to me when someone went to live abroad, despite telling people that she'd gone, I was pestered for years with debt collectors, because mine was the last known address.(posted 7860 days ago)If you just send the letter and S/D back then it might not be the end of the matter and you'll still be pestered. I'd suggest you go and see a solicitor and get them to send a letter in the strongest terms telling IGI to get lost - it need not cost much - about £50 if that. IGI are more likely to pay attention to a solicitor than you.
hope this helps.