Just because the UNO headquarter is in the US, it does not mean that the UNO belongs to the US.
Ownership has its own unique characteristics:
I own S class. I have its papers, Even my wife is not allowed to drive it.
I can sell it.
Can the US sell its product/service = Internet?
No.
Can the US tell other nations to not use it ?
No.
What is the ownership then?
View attachment 322072
Depending on what you are counting as "Ownership", and you are confusing something abstract (such as internet) and something tangible (such as a car)
Ownership can either be tangible rights (ie, sell, trade or transfer of an actual item) or intellectual right (ie, develop, control and management of an item or concept) in this case, the US owns the internet as in intellectual right.
Not everything is tangible, internet is not something we can touch, and hence all ownership goes to intellectual properties, ie, a country can control which country use what and usage in what capacity..
Can the world use the internet without IP, TCP, DNS, DCHP? What if Microsoft (The intellectual properties owner of TCP) suspended the world wide service agreement of TCP and only allow company in the US access to TCP technology? Can you still use internet in China, India or Pakistan? What if ICANN suspended the right to give and access domain name outside of the United States, can you still access yahoo.com or any website in India, Pakistan and China? What if IANA decided to roll IP number back and only allow allocation to US company only, would you still be able to use IP in Pakistan, India and China?
And between Microsoft, ICANN and IANA, these 3 companies control most of the internet flow and manage their product to service the internet as we know it, but get this, both ICANN and IANA are both under contract with the United States Department of Commerce. So, to answer your question
Can the US sell its product/service = Internet?
Yes, since IANA sell, control and manage IP number as a block, if IANA decided not to sell IP number block to any country, you cannot use them and since Internet is build upon IP, so
YES, they are the one selling you internet service in block. You cannot use internet without both DNS and IP.
Can the US tell other nations to not use it ?
Yes, IANA, ICANN can suspend user agreement upon both DNS and IP to other country, IANA and ICANN do not need to tell other nation not to use it, they simply stop their product from being use in other country, they can simply stop supplying Domain Name and IP to a third country. Again, IANA and ICANN both in contract with the US government, hence US Government can technically stop any country from accessing the internet via DNS and IP
Again, as I said, you can still access peer to peer network without DNS, DCHP, IP and TCP, but that would not be the same as the concept of "INTERNET", it would just be a close circuit network, which one network would have to be independent to each other.