How Do I Fix My Xbox Live Connection?

My connection to Xbox live works and all, but a lot of the time I can't join my friends due to connection issues. So I decided to spend 3 hours trying to fix this and all Telus did was tell me to open some ports on my router, and it'll be fixed. Unfortunately I still can't connect to my friends games. The Rockstar games can't even do matchmaking for me, it always gives me the message, "You were kicked from the session due to connection issues with other players." This especially pisses me off because I can't connect to ANY matchmaking games while my friends can do matchmaking with ease. All I would like to know is how I can get my connection to be normal.
My router is a Siemens Gigaset 48, and I am wired from that into my xbox. GOOD LUCK!

Suggestion:

Hmm… this is odd. What sort of internet connection do you have, anyway?

Perhaps make a query at a tech support website.

If I were in this situation, I would try a different modem. If this doesn't work, yeah, try contacting a tech support website or a person that's smart with internet connections.