Check with the phone company to see if the above applies in your situation. Another cause could also be the connectors and wiring in your house. Following is from a user or a K56Flex modem. Capable of receiving at up to 56Kbps, and sending at up to 31.2Kbps. Due to FCC regulations on power output, receiving speeds limited to 53Kbps.
Actual speeds vary.
Requires compatible phone line and server equipment. Complies with both the V.90 56K standard and K56FlexTM technology protocols. Test your phone line here for compatibility before you buy.