VTI & VXUS dividend double taxed

Via Saxo I have invested in VTI and VXUS. A couple months ago I did submit the W-8BEN form and it was accepted. Now when I received the dividends I still see two times 15% deducted. I believe this is incorrect and should only be 1x the 15%?

Any tips how to proceed because via saxo I can only talk to a robot...