I understand that Safari sometimes redirects you to websites that give you advertisements for gift cards. It's important to make sure that you can use Safari without any issues, so I'll be happy to provide some help.
First, I suggest closing the Safari app using the steps in this support article:
How to force an app to close on your iPhone, iPad, or iPod touch
Then, use this support article to clear the history and cookies from Safari:
Clear the history and cookies from Safari on your iPhone, iPad, or iPod touch
Once you've done both, test and see if you get the same result.
Best Regards.