Tv freezes picture, tech switched box, still having issue

What is the main cause of the lag issues with my tv picture and internet. This has been an on going problem since i purchased a year ago and more than likely i will not continue being a customer if the problem can not be fixed. The tech came out and switched the gateway it worked fine for the time he was here (of course). The most annoying thing is playing online games on xbox one and as soon as the lag comes it disconnects me from the game. Please do something about this issue