Slow speed to no connection

Been having these issues for a few weeks. Been trying to figure out myself.. I was getting no internet or dial up type speeds so I changed the initial splitter that goes from the main line to the phone modem and cable box and that seemed to help only if I have one of the lines connected directly to the internet modem.. receive power level 0.1dBmv  SNR 29.4 Db  and Transmit power  50.2 dBmv... internet seemed fine but I didnt get a chance to do a speed test. Reconnected the splitter on the tv line so I could have internet and TV and could not reconnect to the internet. Moved the modem to my bedroom, where the phone cable comes in to the phones modem and I was able to put the phone modem and my internet modem on the line and be able to get both... I didnt write down my data from my check but I believe it was receive -4.7dBmv  SNR 32dB  and 53dBmv... and they are supposedly within the minimum and maximum values but i am getting only 2-3Mbps download and 2Mbps Up... any suggestions? I noticed my modem Scientific Atlantic DPC2100 in no longer sold or rented by Cox and I think is docsis 2.1 but I never had a problem with this modem before... Also when I do the cox speed test it is saying i am not on the COX network... how is that possible?