It sounds like you have more than 1 VoIP line registered to your Gigaset phone.
You will need to login to your Gigaset web interface to check that your correct phone line is set up to make outgoing calls and to receive incoming calls via the Gigaset web interface.
To access the Gigaset Dect Phone N300 or N500 Base Station web interface settings please click here.
To access the Gigaset Desk phone web interface please click here.
If using a Gigaset Dect phone when logged into the Gigaset Base Station web interface you will need to follow the instructions as shown below:
1. At the login page enter 0000 to login
2. Go to the Settings tab.
3. Please check the Telephony, Number Assignment option and make sure that 'for outgoing calls' is selected against your VoIP line as shown below:
4. Click on Set to save this setting.
5. Please logoff to exit.
If by doing the above this still has not resolved the issue please contact our Support Helpdesk.
If using a Gigaset Desk phone when logged into your Gigaset web interface you will need to do the following:
1. At the Gigaset web interface login page please enter in lower case ‘admin’
2. Go to Settings > Telephony > Connections
3. That page will list the phones lines that are linked to your desk phone
4. Next to each line there is a tick box that says "Default Send Account"
5. Just tick that box for your preferred line and click Save at the bottom of the screen
6. Please make sure that you logoff to exit the Gigaset web interface.