Debt I don't know of

I have recently been receiving threatning smses and calls from a company called HTN Attorneys regarding my Wonga Loan which is was showing paid up on my credit report for 2years, I have never been contacted by Wonga and I never changed my details. I am still shocked as to why after almost 2years I am now being chased for this debt, to make it worse it is not Wonga who is contacting me but they have already handed over my account without even notifying me via email. Now after 2years my credit report shows I am in arrears. I want to know why did it take you 2yrs to chase me for this debt and why was I not notify when it was sent off to the attorneys. I did settle this account please check your records and update my credit report.