You've not told us whether you're using a PC, an Android device ot something else. (The instructions for disabling Google Safe Search vary between devices).
Are you following the instructions on this page?
https://www.lifewire.com/turn-safe-search-off-4582268
Have you done anything to clear the cookies from your browser in between disabling Safe Search and finding it turned on again? (If you're using Google on a PC, when you're not logged into your Google account, your browser will need to use a cookie to remember that you want Safe Search turned off. Some people, like me, have their browsers configured to delete all cookies at the end of each browsing session).
ISPs can also automatically use Google Safe Search as well, especially if a customer has signed up for a 'family friendly' service.
Remember that there are plenty of other search engines as well as Google. Try Yahoo, Bing or DuckDuckGo instead.