Apparently the companies in Greece have very bad lines and when you pay for 25Mb/s they give you less than half of that. In the contract it actually even states that as long as it’s above 9 Mb/s it’s not a violation of contract. I was wondering if buying a better router instead of the one provided to me would make a difference
Your connection is probably some species of xDSL (do you plug your modem/router into a phone port?) which falls off very badly based on distance from the distribution point, so it is unlikely to be the fault of your hardware unless it is twenty years old.
I suggest looking into Starlink or 4G/5G fixed wireless, which have their own downsides (latency, basically) but will absolutely do better than 25Mbs.