either slow download speed 200k or intermitten connection

Starting from this weekend, I experienced either slow download speed 200-300 kbps.  The modem has been reset multiple times either at my side or remotely through reps.  Still slow speed.  Sometimes I did get the normal download speed but within a couple of minutes, the download was gone or below 1M.  ping result got 100% lost, good time 10-20% or even 0%.  I am suscribed to 25Mpbs combined with phone.  Since I do not need phone except for security company, I added my Scientic Atlantic modem used to work well with Cox and dedicated it to internet only.  I did get good download speed, at least >10M.  But I got intermitten internet connection.  Mostly I can not run back to back speed test (speedtest.net or speakeasy or even a single speed test.  either stuck in download or upload test.  My internet got disconnet within that period and then comes back.  I am working at home, need stable connection.  This really hurts. Will have rep come to check tomorrow morning.  But any suggestion would be help.  Just ran speed test and my download is 2.05Mbps and upload 14.22Mpbs.  This is using SA modem.  Internet got disconnected when running the second time. Back again.  All these happen during the time I am writing this post.