Re-identification of your Prepaid card

Hi, I got asked to log in with my Belgian ID and register myself so that they know that the pre-paid card is connected to me. I logged in with my Belgian ID but then the system says that it doesn't recognize it my number as a pre-paid car. It is a Belgian Proximus number that was formerly connected to my old employer that I had changed to a pre-paid. I live now in Switzerland and can't visit Proximus to have it sorted on site and there is no email option or chat option.I really need this number active since I visit Belgium regular.

You registered your Pay&Go card almost 18 months ago with a bank card. The law requires you to identify yourself again, otherwise your card will be blocked on 10/11/2020.

When I enter my number I get:

Not a valid Number

Please enter a valid Pay & Go Number

My number is 0476383734, not connected currently since I am not in Belgium.