Hi jasekent,
It is not unknown for spurious entries to be placed on credit files.
You should contact orange and try to resolve this directly. You should also contact Experian to notify them that the marker is in dispute. Experian will not remove it without notification from Orange but should place an "in dispute" note against the marker.
If you can resolve this with Orange then all well and good.
If not, then the Information Comissioners Office (www.ico.gov.uk) are the regulator for the Data Protection Act. They should take up your cause and deal direct with Orange. You will need to get some detail from Orange to make a complaint and the process will be slow as the ICO is experiencing a heavy workload at present.
The alternative is to seek a court order for removal of the marker (injunction). You can threaten to begin with but you may need to go to court for this.
The above is a reasonable sequence of actions:
Talk to Orange & Experian.
Go to the ICO.
Enforcement via injunction.
Since this constitutes identity theft, and the consequences can be severe, you might want to discuss this with the daughter before to take a more heavy handed approach. Also, if it isn't the daughter, you might want to contact the police/ CAB and get advice on how to prevent any further activity. If it is an unknown party using your identity then there could be other activity that should be blocked before it becomes more serious.
Not wanting to scare you but if you go OTT now, it might prevent more heartache later.
Hope this helps
S