Using Browser Configuration
The process to solve this from happening again had two steps.
1. Clear Browser data. Using Google Chrome (my case), in the “Clear Browser Data”, there are plenty of options: password settings, browser history and cookies controlling the ads, which we want to delete.
2. Block Cookies using the browser settings configuration.
These steps solve the problem in a short-term basis, however many pages do not allow navigation unless cookies are activated. Nevertheless, even if the general settings block cookies, they can be activated individually in those websites which require it.

Browser cookies history

The problem I faced was due to recurrent searches about the same topic. I spent 3 days looking up transport tickets from city A to city B for date D, and used several travel service web pages (skyscanner, goEuro, kiwi…). Even after I had booked and payed my tickets, I was constantly seeing adverts related to trips from city A to B, transport companies with best pricing, other trips on date D and many other topic-related adverts. These pages (mostly every website) use cookies, and even if you do not accept them, by continuing with your navigation, you’re indirectly accepting them.
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