Extremely slow speeds

Hi! on 10-18-19.. there was a Comcast outage for about 6 hrs when it came back up my download speeds were averageing 50 -70mbps, i should be getting 600mbps.. I was getting that before the outage.. A tech came out, changed out modem, ran a new line from the pole, changed splitter.. put on a moca filte.. nothing changed.. a Supervisor came out and said levels were fine.. still nothing changed.. cal;l tech support.. still nothing changed.. I really need this fixed.. i  really think something is awry after the outage... tech said my codes are correct for 600mbps..  but something is capping my speeds or smething is crossed up.. I need help here