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I am trying to get to the phone tools to view call history and messages. When I click I either of those, I get the following:
Your browser sent a request that this server could not understand.Size of a request header field exceeds server limit.
I have no way of getting to missed calls.
I have experienced the same problem, only in Firefox - it has continued working in Edge. When I selected "Call history" from my account page, I received the same error message as the original poster. I solved it (at least for now) by going to Firefox Tools->Options->Cookies & Site Data->Manage Data, entering "cox" to select all cookies with Cox in the name, and then "Remove all shown...".
Yeah, that still works. I previously posted in this same thread to delete cox.com cookies to fix this issue. Call History has worked every time I've tried it since then.