And how does dark matter explain this? If you cant prove it even exists?

Dark matter is not an explanation, it's a placeholder. What we've observed is a gravitational pull we can't explain, to which there are three possible explanations:

1) Our formula for gravity is wrong

2) There is matter of known types we haven't detected

3) There is one or more unknown types of matter at play

We've looked hard at modifying the theory of gravity but all the proposed modifications cause it to fail other results that are correct today. So assuming the formula is correct, we can estimate how much mass is "missing" and we label this dark matter. And then search the particles we know to see what other effects they'd have, to get some upper bound on how much of the dark matter it is. And then we find it doesn't add up to 100%, not even close. Most explanations rush this part and go right to all the potential candidates for what the rest is.

So we've found more of the traditional matter, that's neat. We know it's out there, we don't know exactly where and how much. But we know it's not enough to explain everything, not in the places it needs to be. I'm not sure how to explain it in a good way, it's like proving that you can't go to the moon with a horse and carriage. It's not about how many horses there are, there could be an infinite number to give you infinite horsepower and it still wouldn't work. You need a different kind of propulsion. Same way with dark matter, no matter how much traditional matter you add it doesn't work. You need something else.