Slow DSL Speed

My plan is DSL-6000. For 2 months, I am only getting max.2 - 3,5MBPS. Technician said no problem with Router and Line. For the first time, when technician reset my DSL Connection I got full 6MBPS speed. But after 1 week again same problem. Later, even if the connection is reset, no difference in speed. What could be the reason. How my DSL speed is increrased?