returned items from customs in Denmark

[staffrobb]

I only randomly have to send parcels abroad, I sell books so they're not excessively large. I sent one to Denmark (22/09/25), Royal Mail tracked & signed, with a correct CN23 customs form as it was valued under a tenner. It arrived back today (28/20/25) with a sticker "Returned unauthorised duplicate use of barcode". Previously I've had a similar parcel take a month to get to Dublin. Am I doing something wrong? I've sent loads of post overseas over the years with no issue, why now?

[john1297576]

Who marked as “returned”? Royal Mail or Danish Post and what bar code are they refering to.

[*vyolla*]

I've not come across this before, but if you Google 'CN23 Returned unauthorised duplicate use of barcode' it says that it's likely a system error, and to contact RM or your Post Office (if sent from there).

[staffrobb]

After finding some one actually in the know at my local Post Office it transpires they don't use the CN23 customs docket (the one with the bar code) anymore. If you send a parcel abroad with  any form of barcoded tracking docket or not, you have to use the CN22 with no barcode. If you send a parcel untracked the P.O. should have a separate barcode sticker they will put on it. As I had some old CN23's I was using them, apparently this is a no no, with the tracked docket & the CN23 it was one barcode too many. Hope this makes sense.

[*vyolla*]

Yes, it makes sense, but this changed a good while back and your Post Office really should have noticed it, I feel.