have you tried to do hard reset the modem??? can you get correct ip address on the local area connection, like 192.168.1.X(1 http://www.tp-link.com/en/article/?faqid=116

follow the instruction below to do some troubleshooting , updating the firmware, set correct dial number and APN etc. http://www.tp-link.com/en/article/?faqid=400

it seems that the TD-W8951ND can only wds with the TC model such as TD-W8951ND or TD-W8961ND according to the chipset . see instruction below http://www.tp-link.com/en/article/?faqid=327 for you...

make sure you have extracted the zip file you downloaded, upload the file named ras into the modem

you may try to fix the DSL modulation type to ADSL2+, it's under network, DSL settings.

there exists hardware difference between Annex A and B, so i think it would be better to exchange the model just in case.