DMC refuse to remove account which I disputed and was in my favor

One account was sold to 3rd party which is DMC. I disputed this account with VCC and the dispute was in my favor. I was informed the account will be removed. Since then I have send several emails to DMC with a section 609 letter requesting them to validate the account. DMC can't validate the account and refuse to remove the account from my credit profile. I have send several emails to Experian as well where I raised a dispute. DMC in return rather keep sending me sms's to make arrangements. I know this is a tactic from them to let me acknowledge this debt. I have chatted on whatsapp with DMC and I informed them that I do not acknowledge this account. They still refusing to remove the account from my name. To the public if you get a call from DMC for debt, please do not acknowledge the debt.