slow internet after technician replace filter, t3 and t4 time out errors

I use to have a excelent velocity and good connection, but i buy a modem to stop paying renting fees, the modem is the netgear 450, exactly the same i has before.so i take my old modem and return it to cox store and then set up the new one with help of cox csr. And all was perfect but two days after that, a technitian come to replace a filter out side my house then the nightmare start.

Videos and movies , even a small  on facebook, tweeter etc , last to start and buffering. Hoo my veloscity is 50mb. I can  not play multiplayer online cuz the connection is not smoot. I already made like 5 calls to cs and they check signal , modem connection and some things more and they said everithing is ok, but my internet still ** some times

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