You don’t say when that was.
The 20€ limit was reduced to 0€ from 1 July 2021. The UK similarly removed the £18 limit where there were no customs and other charges. All those imports from China, Channel Islands, etc which were under the limit now have to pay VAT, etc .
See my earlier post for detailed information on the new regulations which included:
This is the EU document on Import One-Stop Shop (IOSS) IOSS which details what sellers need to do with regards to declarations, VAT, duties, etc. Companies such as Amazon which provide a marketplace are responsible for sellers through the marketplace. Note there is a different process for items valued over 150€. A simple fact sheet https://ec.europa.eu/taxation_customs/system/files/2021-02/e-commerce-uk-factsheet_en.pdf
Again, there was a very clear customs declaration on it and again there was no tax/duty/vat to pay, so I can only assume that either the local post office loves me, or there is a certain amount of latitude in implementing the regulations !