Unknown devices connecting to home network

[saood88]

I have recently installed xfi app and to my surprise I saw a lot of devices connected to my gateway. Apart from my own tv, chrome cast device, iPhone and samsung phone there were over 20 devices connected. These unknown devices includes-
1. Multiple IoT devices
2. Expressi devices
3. AmazonTE
4. Amazon firetv
5. Amazon echo series speaker
6. Technico device
7.Many ESP devices
8. Wyzecam camera
9. Multiple Ipad
10. Apple TV
11. Iphones

I have taken below steps already:
1. Updated wifi password
2. UpdateD both wifi name and password
3. Factory reset setting of router.
4. Hidden the network

No matter what I do, these devices keep on connecting to my router/gateway.

I am seriously concerned about security

[hollylynne]

I just had 9 new devices connect to my network in the past hour.  None of them should have happened.  7 happened while I was working, so I rushed to change my password and then the other two almost immediately connected as well.  I'm very concerned about security as well.  

[TomSoLo1991]

I had this exact issue back in April of this year. Had about 30 unknown devices causing havoc and ruining speeds. Don't waste your time resetting the router, changing pws or getting a new modem.
First what you need to do is go to where your your coax cable first enters your home. Between that main line and the one going into your home (or between the main and splitter) there should be a POE (point of entry) filter. Or aka a MOCA filter. It's about 3 inches long and normally costs under $10. If there isn't one there, just pick one up and install it yourself. Comcast will try to charge a massive fee to have a tech do it even though they should have done it when the internet was first set up. After the filter was installed all was good with the internet.
Basically what the filter does is block your modem from feeding back into the main line and blocks your modem from receiving feedback from other modems. If log into you modem via 10.0.0.1, you'll probably see that sometimes your router name will be different. And this is the feedback from the other homes. So get the filter. It won't lower your internet speeds