fingerprinting isnt about IP and browser/useragent only, it also detect OS and hardware specs, location gps (especially on phones), region, language etc.
encyclopedia.kaspersky.com/glossary/fingerprint or fingerprint.com/blog/browser-anti-fingerprinting-techniques explain more about it
i am guessing they likely collecting data pattern, which mean new acc. for 2nd time, they will let same hardware with different IP
but next time they detect same os+hardware, the blocked it
bypassing with phone is more successful, because phones have same hardware specs, and MAC address usually automatically random generated, which if they aggressively blocking, it can be also effecting many more legit user
did u test ur device with fingerprint test like
https://fingerprint.com/demo/
if it detected same visitor, then u need to figure out how to make it detecting different visitor
you can try change region + language to check whether it is working or not, plus to know how far fingerprint data they collecting
if anything dont work anymore, well time to pay i guess