Keep threads regarding the above clearance problems to this thread, for An Post/Addresspal only. There are separate threads for the courier companies in the courier forum.
IOSS numbers need to be on the parcel and in the electronic declaration. If An Post clear it and pay VAT, the customs entry will need to be amended, and as they won't get paid to do it, An Post won't be keen. This is for eBay and Aliexpress traffic. They all know about this for a long time, so they should be your first point for complaint.
The An Post/Customs system seems to have a blind spot for books. SOME are zero rated, but not all. They need to have the proper taric and correct description.
Anyone clearing goods has work to do, and it isn't included in the postal price. It's a fact of life, do not come on here to moan about it.
The email address to query VAT/Duty payments with An Post is: ecommchargequery@anpost.ie