You can contact them at any time. They are a digital insurer, so the best way to contact them is through their website or by sending them an email.
But you can also reach them by phone at +32 2 588 25 50 or send them a letter to the following address
QOVER - Customer service
Rue des Palais, 44
1030 Brussels - BELGIUM
They speak French, Dutch, Spanish, Italian and English.
If you choose to call, please note that they are available Monday to Friday, 9:00 a.m. to 4:00 p.m (CET). This is a relatively limited schedule because they prefer electronic contact.