Have you considered the possibility that what the speed tester is telling you is true: there is a limiting factor somewhere along the Internet path between your client device and the OVH speed test server. It's an end-to-end test so you're testing everything in between. Small levels of packet loss anywhere along the path can limit the rate at which TCP sends traffic: the formula is
here.
If you get full speed to other speed test sites elsewhere on the Internet, then that probably rules out a problem at your side. But that begs the question: unless you intend to make use of a service hosted at OVH, why do you care about the quality of the Internet path to OVH?
TBH, I don't really understand why people are so keen on constantly speed testing their broadband connections. Just use it. If you observe a problem, then doing tests may help isolate the problem and provide useful information to your ISP when you report the issue. But otherwise, you're just adding to Internet congestion.
I do wonder what motorway congestion would be like if everyone kept driving back and forth to Barnard Castle just to check their car and their eyesight