Are you using a wired or WiFi connection? If WiFi, try with a wired connection.
If the speed is correct with wired, then you know you need to investigate your WiFi settings and performance. The first thing to check is to make sure you're using WPA2. There are lots of helpful posts on the forum about getting the best WiFi speed.
I see the original post is over a year old but no resolution. I have the same problem. Kept getting disconnected from the internet so they replace the Box on the out side of the house (I think it is called the ONI or ONS box) Also replced the ends ona coule pieces of coax and replaced the splitter. Problems continued. We had the Actiontec MI424WR Rev D and were always able to get our speeds that we pay for (50 down and 25 up) often even more! Today they sent us a replacement and it is an Actiontec MI424WR Rev I. I am thing wow what an upgrade, now we can try out the GIG-E card in our new PC and we even have Wireless-N. Yup sure did to the tune of 5 mbps down and 18 mbps up. Swapped out for the old and got our speed back. All of the speed tests are wired using the same PC at the same location with the same wires. The only thing different was the router. What gives Verizon? Guess I owe tech support a phone call in the morning.