Debt Repayment on Credit File

Hello Everyone.

I was a sole trader in 2005 running a small business and at the time, I had opened a commercial business account with Bank of Scotland.
In 2008, I had to close the business down and could not pay the overdraft that was still left outstanding. As I owe them and I still owe them, I have been paying them £40 a month.
Over the time, the account was transferred to Hillesden Securities, known as Cabot Financial. Cabot Financial writes me letters informing of my up-to-date account statement etc. I have been still paying them and we will clear this debt soon.

This account never showed up on any of my Credit reports with mostly all known credit referencing agencies.

However, I received a letter from Cabot financial state that they decided to deal with my account directly and will show as Cabot financial instead of Hillesden securities, etc. The bottom right pane of the letter states: "This account may be shown on your credit file and may be hard to obtain credit from other lenders".

I have been paying them since, and never missed any payments in my arrangement and I don't want to write this debt off as it is my debt and I truly am responsible for it as I used the overdraft for the business.

Although I have never seen this marked on my credit file since 2005, can they still mark this account now?

I thought accounts such as this one, are dropped off from Credit reports after 6 years whether or not payments are posted to the account, or whether or not you have acknowledged the debt.

Thanks
Please classify.