Consistent ping fluctuations. Dont know how to resolve with isp

Im using cox cable. Realistically my ping should be around 30-40 ms. I usually sit at 41 ms but lately it has been fluctuating. Over the last week it constantly jumps from 40-60 and ocassionally bounces up to the 100s. This makes playing skillshot based champs extremely frustrating. ​ I thought it may have been my modem. So I called my ISP. They ran a check and stated the report on the hardware was critical and it needed replacing. Fine. I had a backup. I connected the back up modem. Got it attached to the account. They ran a report and said it looked fine. However, when I mentioned issues with the ping they seemed to have no idea what I was talking about. ​ ​ I start up a game just to see and now my ping is even worse. Its up to 50s and proceeds to bounce much more erratically than before. ​ The backup router is one I used about 18months ago and it was brand new at the time. It worked fine then and I received consistent speeds with the same ISP two streets over. Ive tried using new CAT5 cables. Nothing seems to work. ​ A similar problem happened to me when I was in the UK using Virgin (im now in the US and playing on NA server). I had a prolonged issues with my ping, which eventually turned out to be a major network issue that needed resolving in the area (however I received a nice refund). ​ This time around I have absolutely no idea what to say to tech support to figure out if the issue is on my end or if it is them.