Very high return by customs from Germany

Hi sellers
I have had a high return percentage from Amazon Germany.
All the other market places seem fine,no problems.
The returns are due deficient cn22 form.
It is low value goods around £10 per average sale.
I send via royal mail oba.
I manually feel in the cn22 form with the ioss number.After a few returns I have added the order number for each order as well,but still getting lots of returns by custom.
French,Spanish and the rest are totally fine.
At the moement I had to close the account because it was getting out of hand.
I was wondering if any one had similar issues or if I can get any tips from sellers who manage to send to Germany and get through customs.
Thanks in advance