Does anyone know how I can stop my units being sent to customers outside of the UK please? And how to stop them being returned and stored in DE and ES?

So for 2 years, Amazon has been sending the occasional unit to DE or ES. We then have to remove or destroy these units because we only sell in the UK. Amazon have checked all of our settings and have confirmed that no units should be sold or sent outside of the UK.

However, it has happened again and we now have 3 units in DE and 1 unit in ES.

Amazon state...

"Please note, when returning an order, customer will be asked to return it to the closest Amazon Fulfillment Centre which might not be in the UK as in theses cases."

On checking, I find out that these units were sent from the UK to customers in Dublin, Ireland. Then they were returned to Germany. Yet all of my settings are set to UK only. Am I missing something? Any help appreciated....Thank you.