In order to accurately test your bandwidth you should be connected directly to the ISP's modem. If you're presently behind a router then that may affect your speed. Also ensure you are not running any bandwidth intensive applications (such as P2P software).
Once you've tested your speed accordingly (or if you already have), contact your ISP with the numbers. They'll be able to tell you whether there is a problem or not. It's very possible they only sold you a 1Mb connection. Or their service may have no form of agreement on throughput. You're only going to find out by talking to them.