ISPs may use different ways to fulfill IPTV connections. In your case, I don't see anything confirmed with your ISP. If you just bind IP and MAC when it works with WR841ND, did you try the same...

problem is dhcp, DHCP is switched off but continues automatically assigns IP addresses Why do you turn off its DHCP? TD-W8970B is working as an access point? There is a DHCP server in the network?...

The box is working fine with WR-814ND w/o any additional settings in the router. If so, can you confirm if there are any requirement for the router to make IPTV work? You'd better explain it first,...

Test the device in service center.

W8970 in wireless router mode is different from WR841 and IPTV cannot be configured properly. To make IPTV work, you may buy your own WR841 or some other model...

DHCP server off??? TD-W8970B is not working as a router? If so, you should bind IP and MAC on the main router.