With DSL, it is trivial to see which speed is assigned to you and which speed is the maximum possible on your line. If your measured speed is lower than your "Actual bitrate" as shown by the modem, something must've gone terribly wrong. If however your plan speed ("on paper") is much higher than what is attainable by the modem, that is a fact of physics and you have to downgrade the plan. You cannot oversell DSL, if it says attainable rate is 10240/1024 Kbps, you cannot sell 15360/1536. The modem will literally be unable to connect at that speed.