MijnKPN is for products for consumers. Very likely the number is registered as a business number (probably in a business batch). 

Do you wan't to use MijnKPN to be able to check your bundel? In this case that is only possible via de phone itself.

Instellingen → verbindingen → gegevensverbruik. (with Factuurcyclus en gegev. waarsch. you can make the bundel the same as what you have via your employer)

Hi @Marip_789, welcome to out forum. My first thought is the same thing Peter mentioned. The MijnKPN you've tried isn't for corporate subscriptions. Do you know what kind of subscription your company has? If it is a big one with multiple numbers it will be a corporate account. Our corporate colleagues have a different MijnKPN Zakelijk. I don't know if you'll be able to link this subscription to this. The best thing to do is ask your employer (or their IT department) about the kind of subscription it is.