Hi,
The budgetphone settings that are working in the system all use the "Basic Provider Details". If you are using "Advanced Mode" then I suggest you start by deleting the budgetphone providers in your list.
Then add a new provider with the following settings:
Username 3xxxxxxxxxx@budgetphone.nl
Password <Your budgetphone password>
Confirm Password <Your budgetphone password>
Host sip.budgetphone.nl
Along with whatever other settings you require.
Once again, we recommend deleting any budgetphone providers you may have and entering them in the above format.