intermittant loss of internet service

I believe i am being charged for services that I am not getting.  Continued poor slow service promised at 30mbyts aa cost to me of $45 per month.  I have spent several hunded dollars on new routers which did not help as cable provider says its my routersfault.  I have had tech service evaluations that proved my computer and magic jack were operational having no defects.  I loose internet with cables modem lights showing operational.  Yet with computer or magic jack directly connected by Ethernet to cables modem I still had no service . this gos on for many hours then my system gos back on line.  Contact with charter cable is no help as they deny everything but my neighbors and internet contacts say they have same problems with charter cable company.