It sounds like you've done the normal power cycle, reset, and re-provisioning steps, so I'll focus on some less common issues.
Check to see if they have put filters on the cable line. Your service line should be tagged as having a cable modem inside. If not, they may have done a sweep in your area and added filters to block TV channels you're not supposed to get. These can reduce (or block) the signal bands required by your modem. It shouldn't happen, but it does. The other is the line splitter coming in. If it's flakey, it can reduce your signal strength.
One last possibility. Has it recently rained (hard)? Moisture in a compromised connector or cable outside can also kill your signal strength. Until it dries up (which can take some time if it's condensation inside a connector) the signal can be pretty significantly impacted.
