Hi
I have seen this happen before. A relative of mine has statute barred debt and their debts have continued to be sold on. Luckily they live in Spain and therefore the UK credit record searches are not an issue.
If I were in your position I would make enquiries with the ICO regarding Data Protection issues, the OFT about the conduct of DCA's and maybe also the FOS to see if a complaint could be made about the searches.
ICO link https://www.ico.gov.uk/Global/contact_us.aspx
OFT link http://www.oft.gov.uk/contactus
FOS link http://www.financial-ombudsman.org.uk/contact/index.html
I am not sure Experian and Equifax would be much help if you contacted them. They provide a service to the financial services organisations and would not be willing to block the searches. This problem is currently being reviewed by government and the House of Commons Treasury Select committee. Martin Lewis from Moneysavingexpert is currently on the case regarding this issue, so you could also send him your information via that site.
If the ICO, OFT or FOS were willing to take on a complaint, this may be the only way to resolve this. But it will be an uphill battle which is not going to be quickly resolved.
Huckster