Debt selling

Good day<br> Woolworths Visa Credit Card *** ES Thomson account was handed over to Mooney Ford Attorneys in 2012.The account was fully paid and received a letter from Mooney Ford that acount been settled in full and will notify Woolworths.On 27/06/2012 another Debt company D & C Collection Service *** phoned to say that I still owe Woolworths.How can Woolworths hand over my account to 2 different companies???I told them that my account been paid up with Mooney Ford and please not to call again.Believe it or not 3 YEARS LATER on 09/07/2015 D & C Collection Service phoned me and told me that I still owe Woolworths.Don't understand.Will someone please explain to me what is going on?????On the system my account also still show LEGAL where it supposed to be CLOSED!!! I need to know what is going on please!!!