netgear r7800 internet not working after iptv option is enabled

Hi,

Today the local supplier of the internet tried to install TV using my router. It requiries IPTV to be enabled. Internet were working fine. After we have enabled the iptv by vlan tag, the TV decoder was able to connect and properly decode TV channels. BUT I coudn't force the router to connect to the internet. It was saying all the time ERROR - no internet connection, no matter how many times I have restarted the router. After we disabled the IPTV the router was able to connect to internet again with no problems.  My connection to the internet is resolved automatically by the netgeat while it has wan connected to the provider gateway device (fiber). How to force the router to connect to the internet while IPTV is enabled on netgear r7800?