there's a statement like "Advertised speeds are not guaranteed". What did they tell you for your area? DSL is distance limited and the farther you are from their facilities, the speed drops. It's just the physics of the telephone cable pair.
This is the same reason that data transfer across a LAN running at 100 Mb/s will not actually transfer at that speed. It's all advertising hype.
Have you called them and complained? Sometimes there are faults on the cable pair that can be repaired. But not until you complain and they test the line.
I have Verizon DSL and my download speeds are nowhere near what is advertised. My last speed test showed a download speed of 740 kbps and an upload speed of 120 kbps. This was described as "90% worse than typical Verizon service". Is there anything I can do at my end? Verizon's slowest advertised speed is 1 mbps. I'm using Windows XP and my modem is Westell model E90-610015-06.