Speeds tanking at night, 7mbps

Hi everyone,

I'm having an insanely frustrating issue maybe someone can help me troubleshoot since Comcast isnt the least bit concerned with actually helping me solve. For at least 2 weeks now my speeds are extremely slow. I pay for the 300mbps speed and was told that 150 is appropriate and expected for WiFi. I'm not usually home during the day so I thought that these low speeds were constant. I'm seeing anywhere from single digit speeds to 15ish at night. At some points I cant connect at all.

I decided to check our neighbors Xfinity hotspot that's open to see if it worked. Seems they were having a similar issue, very slow, sometimes network was not visible.

I've called comcast and had them restart my modem a thousand times, had someone come to check outside because I figured it was something going on in the area. They sent someone out who insisted there was a low hanging cable so someone would have to come back. The guy came back today and said all the cables looked fine. I had him come inside to check my modem since he insisted it "must be my modem" and sure enough the connection was fine.
He told me to try changing the channel on my router (not sure how to do this) and see if it helps. Gave me some baloney about how different things in the area give off frequencies that might interrupt my signal.

Is this true? Why all of a sudden is my internet trash then in the past 2 weeks? Is this a comcast issue that they don't want to admit to?

Someone please advise. The only time I use my internet on weekdays is at night when I'm home from work, and I'm tired of paying so much for such bad signal.

Thanks in advance!