It might be because your router hasn't been reconfigured to work with MTS. In its factory configuration, a router plugged into another router creates what's called a double NAT. I'm not a networking expert, only self taught with 7 years experience installing MTS. I've seen MTS' generic instructions work, but others here have posted alternate ways too. If you look through this MTS section you'll find them fairly easily.
Authorized Service Provider (Contractor) for MTS Allstream. Any views expressed are my own.