Slow since adding TV

I added TV to my existing phone and internet last week and my connection seems considerably slower.  I should be getting 50mbps but the Cox speed check to Atlanta regularly shows 10-20.

The contract technician changed my existing modem (not sure what kind it was but it looked like a DPQ3212) to a TG1682 if that makes any difference.  He also changed the cable from the street to my house because he said it had a lot of noise on the old cable.

Apart from slower speeds I'm wondering if it was necessary to change the modem as I already have my own router.

Thanks.