I assume you have Windows 10 Home. For some crazy reason, Microsoft has removed the option for Home editions. I myself had this issue and the only way I could stop the updates are by disabling the windows update service thread.
Method 1 (If you are using a Wi-Fi connection)
Set your Wi-Fi connection to metered.
Settings > Network & Internet > Advanced options > Set as metered connection
Method 2 (If you are not using Wi-Fi)
As Ethernet connections cannot be set as metered (another design flaw), the only option is to disable the windows update service.
Go to search and type “services.msc”. Now select Windows Update and click on stop. Once the service stops, right-click on the windows update service and set the startup type to disabled.
However, remember that you will be missing the critical windows updates forever. To update again, set the startup type to automatic and start the service. Also, disabling this might affect the windows store experience. Hope it helps!
