This sounds like a problem a lot of people have
You can also run tools like speedtest.net which show how much bandwidth your connection has and latency (to their servers). Run this periodically at certain time intervals and save the results. Your ISP may also have it's own tool to measure this (comcast does).
The other thing you can do on your end is run a network monitoring tool that, depending on how you set it up, can measure latency times to certain sites at certain times of day.
The problem with any of this is 2-fold. 1) you can only run things on your systems/network, and a lot of the problems may be the networks or sites of the games servers, your ISPs, other sites, or intermediate networks that the traffic is flowing on, so you can't directly find it, and your ISP has no control over it if it's not on their network. 2) Read your contract with your ISP carefully - changes are your ISP does not promise you any given service level, instead saying something that boils down to "best effort". So they may not even want to help.
Still, try monitoring your latency/ping times and report the numbers to your ISP, see if you'll get someone who can help.