I tried to configure MT to work with our ADSL line too. I know how frustrating the thing can be, so I try to reply with what I know, but I know little so far, so actually I will not probably help you to solve your case.
The trouble I had was with static IP we got for our ADSL from our ISP. I wanted it to appear on MT. I set MT external interface and ADSL into bridge, but not luck. The trouble is, that those ADSL modems/routers are most of the time piece of crap, so you can't be sure, that under the hood, some functionality is supported.
You can look at MT's documentation called RouterOS How To List - there is an example for xDSL.