Hi Gabriel,
Sorry to say this issue comes up a lot with Apple products. Unfortunately there is currently no way for anyone other than Apple to remove an iCloud lock from any Apple device.
Your best bet is to contact the person whose account the iPad is locked to and ask them to remove the iPad from their iCloud account. If it's your own account and you've lost the login information, you can take the iPad to Apple and they'll remove the iCloud lock but you have to have the original proof of ownership.
If you bought the iPad from someone who sold it as being able to be activated, then you need to return it and get your money back.
Sorry I don't have better news for you, but that's just the way it is with Apple products.