You may have accidentally clicked "Watch this topic" at top right which appears when you click Options in the green bar. If you are getting notifications then if you go to that topic you should now see the link as "Unwatch this topic" - click that and you will receive no further emails.
How do I click Unwatch in the mobile version of this site?
The same way - click Options in the green bar then click "Unwatch this topic" which appears above the Forum topic. It worked fine on my phone but if on your phone you have an issue, do it from a tablet or computer.