I'm trying to file a VAT return and it comes up with error message "You must specify a different number. This number has already been used." What do I need to do?

Hello Uschi 👋, Thanks for letting us know of this issue that you're experiencing. Our engineers are aware of this issue and are in the process of being prioritized/investigated. Although this is being actively looked at, We do not have time for resolution at this time. Are you able to send a private message via Twitter/Facebook so we can take some personal details from you and attach you to a case so that you will get notifications on the progress of this issue? Thanks, Becky