Clients are able to unsubscribe after the unsubscription period has already ended – or – Clients are not able to subscribe even though the subscription period is still valid

This means that (most likely during the account setup) you have set the wrong time zone.

No worries, this can be fixed quickly.

Go to — SETTINGS — COUNTRY-LANGUAGE-TIMEZONE and set the time zone to Italian = +01:00 (or the one for your local area).