No worries. Two basic things you should follow to reduce the chances of happening the same issue from next time.
1. Regularly Monitor Google Analytics Traffics
Being an Adsense publisher, it's your responsibility to keep an eye on referral source of traffics. If you will keep getting traffics just from one domain, it may be considered as invalid. If you see any unnatural hits toward your site, you may report it to Google.
2. Use Site Authorization Feature
This feature will ensure that your Ad code will remain eligible to use on your verified domain name only.
Learn more: How you can help to prevent invalid activity
All the best!