IP address is one factor,
browser fingerprint is important also,
There are lots of browser fingerprint use different technology, one of most common is the canvas fingerprinting that others already noted, I suggest you easily check this website,
Yes, Now you learn the reason why got suspicious, Okay, assume your IP address is 100% fine, If the issue is browser fingerprint, how to bypass?
There are 2 ways,
One is old ways, Clear cookie and hides all information as you wanted... just as you did

But It's not the best, why?
Let FB as a sample, those Data-driven companies already have you so much data...even you're not surfing for their website...
You can check this video to know more details!
So, If there are no data get before when you register, the FB will ask you to submit "photo IDs"...or make as suspicious for It's impossible no data got
So. nowadays, mainly use spoof ways to prevent browser fingerprinting,
You check this post to learn more,
https://www.bestproxyreviews.com/how-to-prevent-browser-fingerprinting/
So, not just spoof your fingerprinting, for big data company like Facebook, google, amazon, find some related website (interest related) to surf at first, implant your cookie and browsing history at first, then they give you a "
user portrait", then not suspicious anymore
