Not getting the speeds I'm paying for.

How are you testing? If you are testing over WiFi, it's not going to be accurate. Testing with a device connected via Ethernet over a 1000baseTX connection will be far more accurate. When I test with my desktop, I get over 580 MBPS, when I test with my laptop over Regular WiFi, I average about 72 mbps, and on WiFi 6, I can get up to 450 plus. The issue is, there are way too many things using 2.4 and 5 ghz frequencies. They all cause interference and can slow you down tremendously, as can distance from the router, and solid objects in between that can block the signal.  

But when Cox checks it, it is magically over 500mbps. 

Welcome to the Cox 'service'. This seems to be a normal thing for them. Had them for the past 5 years as they were/are the only choice. I have had to fight with them multiple time to troubleshoot their own stuff to get things fixed. Everytime I get them trying to sell me their addon that prevents me being charged for a service call should it be an issue in my house. Even got charged once when they never even found a problem, got it removed. Normally envolves calling multiple time, have them credit me for everyday services rendered are not what im paying for. Most of my issues were intermittent and could be seen in my modem logs,  but luckily, one of the techs that came out, after multiple mind you, attempts was smart enough to think outside the normal and scheduled to get a line truck out and they both monitored the line for awhile. Ended up find an issue further up the lines that affected me and my neighbors.

Now, my gig speeds, normally 930'ish, is at <400. Thought it might be somewhere between us and the servers that would get corrected, but 3 days later still an issue. Only found out by accident so who knows how long this gas been going on. Thankfully, we have a new fiber company laying lines and are almost to our neighborhood. I will go from paying $120 for shoddy 'gigabit' 940/35, with capped useage to 2gb up/down for $$99 and no useage limits. Wont have to play the 'lock in a deal' for two years then they raise my rates through the roof because my deal expired. 9 times out of 10 the same deal is there, but unless YOU do the work to find it and apply it they will raise your rates. I went from the 500mb(fastest at the time) with the biggest package of channels, 2 years later believe it was about a $70 price hike, dropped a channel packe down to get close to what I paid before, 2 years later rinse and repeat and now i cut TV totally off, despite finding the exact same 'deal' that actually cut my package cost by a couple dollars. They play a stupid 'deal' game instead of just giving their customer a normal price all the time. I can not wait to cut ties with Cox. This includes everyone i know around the whole county, and its the same on our town's community Facebook group. Cox is about to take a HUGE cut to their income once this company finishes laying Fiber here.

Hi wp. The purpose of the Cox Forums is to allow customers to discuss technical topics related to residential Cox Cable, Telephone and High-Speed Internet services with other customers. This appears as if you may need someone to look into your account personally. We would definitely be able to assist you with this. Please reach out to us on Twitter at CoxHelp via DM, visit us on Facebook via private message, or email us at cox.help@cox.com. Provide us the name on the account with the complete service address with a link to this thread so we can get started. Thanks, Lisa, Cox Support Forums Moderator