I called the phone number and my financial instution answered and after asking some account verification questions was able to send the verification. Works fine now.
Hello, i solved the problem (i live in Belgium and using Belfius as bank). First update your phone number in your garmin account (garmin.com) then update there your profile / phonenumber -> select your country or region for your preset number -> then add your phonenumber (i left the Netnumber empty). Then go back to garmin connect to add your desired card. Then use the verification and when you see that they send you a code, go to your app of your bank. There you will see in your inbox the garmin code so not via sms or text :) it worked for me so i hope that it will help you also.