I agree it sounds like a signal issue. Did the tech climb the pole and check your signal at the tap? If you have Cox Complete Care, I'd suggest you continue to contact Cox and schedule tech visits until your issue is resolved. Eventually, a tech will detect a signal issue, if he checks the mainline signal. If you don't have CCC, I wouldn't recommend that strategy because it could get expensive, unless you want to subscribe to the service for three months to get your signal issue resolved. I believe there is a three-month minimum. I know you shouldn't have to pay to get Cox to fix their issue. You might be able to negotiate that and get the $10 monthly charge for CCC removed if it's determined there was a mainline signal issue that went undiagnosed by the first tech.
