I want to speak English fluently and I'm able to spend money and time?

Where can I best invest to learn English (e.g. Private teacher or something?

To everyone who says that who learned English through Netflix

Very good though

I want serious answers

Download roblox, there are a lot of English people and you just look for some with whom you can call

If you have that in your city, go to the School of English. Here in Cologne there's the institute. It's not cheap, but it's worth it. There are courses for beginners up to level C2.