TOPIC: Discount code update not working

I have created a 100% discount code for course instructor to use to register phone-in course applicants for courses that cost money. This controls maximum numbers, and lets the instructor register the applicant without having to personally pay the course fee.
However, a back end administrator needs to change the registration via DT Register/Records to delete the discount code (or substitute a zero percent code), change paid status to No, Payment Method to 'At the door' and enter the amount due.
All works except the discount code field. Even if it is cleared or changed, when saved, it reverts to the original 100% discount code. How can I edit the field.
Please help
Thanks

Hello. We have no order on record for DT Register under this user account. Support must come through the account you purchased with.

Would you please answer the above post as the prooduct was purchased under my account. We are both with the same volunteer organisation.
Macca