It seems that your router is currently set up to use PPPoE, which is hardly ever used in Finland.
This tip tells to go find menu operation mode and over there set mode Wireless Router and select ok. The modem wants to restart, accept with ok.
If this is not enough, check the WAN connection settings and choose Dynamic IP. Some other manufactures may call this mode IPoE, too.
The fact that your computer works without a router gives away that you have an Ethernet connection. Therefore, DSL will not be used. But this is not a problem, as TP-link TD-W9970 can function as an Ethernet router, too. Just plug the Ethernet cable to the WAN-port of the router.
MAC address is best left as default. Telia's Ethernet and DSL connections do not require using any specific MAC address. Only cable modem service requires giving out your modem's MAC address when you sign up for the cable modem service.