With a 50m cable connection, I am surprised you get any buffering at all and it should be in HD. My first thought is the cable connection quality - they may be "throttling" usage at certain times, and sometimes cable internet simply can get bogged down during high usage times by everyone in the surrounding area.
Are you actually getting 50m speed? Have you tried speedtest.net to check the cable internet speed?
If you are willing to do the merry-go-round, call your cable company and double check about your contract to see if it has any kind of speed limit included. Also, if your speed tests are showing you aren't getting the speed your are paying for, is your cable modem updated? If it is out of date, the cable company might replace it for "free" as part of your contract ("might" is the key word...). It is also possible that there is an issue out in the street connections for your cable internet. That has to be determined by a cable tech coming out and testing it - they won't do that until all other options are exhausted.
Good luck! and try to keep a good attitude in calling the cable company!!