Thanks for your post and welcome to the forums. It's great having you on board with us in the Community.
I'm sorry to hear you are having trouble paying off an old account. We're not able to take a payment over the Forums however we would be able to send out a reminder letter of your memorable word if you are still living at the same address.
If you have moved then we can try asking some other questions to pass data protection and once that's done we can reset the memorable word for you which will in turn allow you to call up, pass data protection and make the payment 🙂
Either way, I will need to confirm some information with you so I have sent you a private message regarding this. Just click on the little plum envelope at the top right-hand side of the page to access your inbox.