Gigablast does not stay accessible

I upgraded to gigablast several months ago, but the increased speeds only last a short time and then it reverts to my old 300 mbps speed.  This is an on-going problem that has been tackled by several different technicians (Online chat; in-home service calls) when I have had varying Internet packages.  The last one installed another router (Which is hard wired to Cox) and a signal booster which worked for just a short amount of time (Although it did resolve the problems I had with my tv signal freezing and sound dropping out). 

Each time a tech comes to my home, they say that the signal from Cox to my apartment complex is okay. A field supervisor was the most successful by upping the amount of signal allotted to my apartment. That "repair" lasted until I upgraded to Gigablast.

In November I once again I attempted to get things working again with an online chat tech who re-set my new modem.  There was no change. I got tired of having to address the same issue, so I did not follow-up (My bad).

I hate being charged for an in-home service call when the issue seems to be occurring somewhere between the master control panel and my apartment and is not the result of anything I have done to disrupt the signal/speeds (Today, the speed was about 408 mbps). I have followed all of the recommended troubleshooting steps to no avail. No change.

I would discontinue my Internet service with Cox and would switch to Google Fiber if it would not incur a penalty.

Are there other solutions? Can my account be credited for the loss of speed between November and today?