Both TD-W8970 and TD-8816 are ADSL2+ modem routers.
If TD-8816 works with your line, TD-W8970 should be OK as well. How did you test? Did you try to change DSL Modulation Type on its web interface?
To make them work together, you can connect TD-8816 to LAN4/WAN port of TD-W8970 and configure TD-W8970 in wireless router mode.

But what is the correct connection model to use TD-8816?
Router or bridge?

The staff of the telephone company commented that the TD-W8970 device is not approved in Brazil, only the TD-8816.
The TD-W8970 until it works here, but with constant falls when I'm using for games or downloading torrents. :(
I really enjoyed the TD-W8970 and always buy TP-Link products and do not understand why not work here.

Who is your ISP? Your connection type is PPPoE or PPPoA?
If you use TD-8816 as a modem router, when you configure TD-W8970 in wireless router mode, the WAN connection type should be dynamic IP. Remember to change W8970's LAN IP to 192.168.2.1 and avoid IP conflict.
TD-8816(LAN)----(LAN4/WAN)TD-W8970

Also, you can configure W8970 as an access point. Change W8970's IP to 192.168.1.2 and disable DHCP. It is done.
TD-8816(LAN)---(Any LAN Ports)TD-W8970

If you use TD-8816 in bridge mode, you must ensure that your connection type is PPPoE or dynamic IP because W8970 in router mode doesn't support PPPoA...

Sorry for the delay in responding. :(
My connection is PPPoE, set up the TD-8816 in bridge mode 192.168.0.1, the TD-W8970 is set to 1921.168.1.1.
I connect to the Internet, but my problem occurs with games and torrents in other pages works normal.
My internet is 10Mbps, ADSL2 +
Was looking for information on my TD-W8970, the strange thing is that he has three antennas and is not TD-W8970 B, is this normal?

Please pinpoint your ADSL line specification. Is this ISDN or analog line? Sorry I don't know Brazilian internet providers :(

jimasek Here the line is analog.

Unfortunately the problem worsened, found here in the Brazilian Tp-Link firmeware one, is the same model and version that my modem, TD-W8790 V1, downloaded the file saved the previous version of the modem and did the upgrade, everything went well and after upgrade I can no longer enter the modem settings. :(

Really, I can not access the modem for any LAN port.
Now I will find a way to rewrite the fimware via computer.
Anyone know the program and know the motagem cable for this?
I take risks, given that bought the modem "free market" to you one "ebay" and it came without notice and without warranty. :(

Which firmware did you upgrade? The one for TD-W8970 V3?
Sounds like faulty.
If it is out of warranty, you have to buy a new one. :(

I used this TD-W8970_V1_140613 firmware

I can even buy a new one without problems, but surely buy another brand if it has not repair.

Other brands and models already repaired without problems, both domestic and imported, here in my house until today was only using modems of the brand, but buy a unit cost so high and not receive what is advertised anymore.

I found several people having to make adjustments to use this modem, who faced the same problem and I had to open the modem and put it sinks to work.

In my case I left it on downloading a torrent and when I got each was locked, delisguei and then reconnected the unit and after 10minutes I decided to update the firmware and then the problem happened.

Here in Brazil do not accept service the modem in assistance from TP-Link, have the excuse that is not approved by "Anatel".

So much trouble to just use 2 usb ......

I found a procedure, I make rewriting the original firmware that came with the modem.