my app store wont let me download and says my payment info is wrong but i know that its right. what do i do? how do i fix it?

If you are trying to do it from your phone, try from other sources, like AppleID.apple.com, another device etc.

Change or remove your Apple ID payment information - Apple Support

Check out this Apple document for guidance on how to review your details. Remember, the tiniest of errors will produce a refusal.

https://support.apple.com/en-us/HT203005

If necessary, contact iTunes Support. Scroll to the bottom of the page in the 2nd link.

iTunes Support

iTunes Support – world wide