So your Internet Service Provider (ISP) is some (French?) cable company. I would bet your original problems were not due to Airport issues, but to your ISP/cable box having some sort of interruption.
In the future if this happens again, try turning the power off to the box, wait about 30 seconds, turn it back on and see if the problem corrected itself. You may or may not need to restart your Mac after the power off/on to regain your wireless connection.
On a Mac since 1984.
Currently: 27" iMacs, Macbook Air, macOS 10.15.x,; iPhones, iPods and iPads galore!