Every time I try to install a free app it tells me I got to pay

You need a valid payment method on file with Apple, even for free apps because of in-app purchases. It won't charge you for free apps.

If you have a balance on your account, you need to pay it off before you can download anything else.

If you want to dispute this, contact Apple.

Contact Apple for support and service - Apple Support

To expand on the great info Kurtosis12 gave you.

You can look at your purchase history to see what the charges you owe are from following If you see 'apple.com/bill' on your billing statement - Apple Support

Good advice.

Good advice.