Q: How do i update my billing address whenever i try to update it always shows me your billing addres was declined try another billing addres?

Try these steps:

Change or remove your Apple ID payment information - Apple Support

Refer the article -

If your credit card company's records don't match your records in the iTunes Store - Apple Support

Your billing name or address does not match the address listed on your credit card statement. Any discrepancy in punctuation, abbreviation, or capitalization can cause errors, which might prevent you from purchasing from the iTunes Store. If you moved, or if your zip code changed recently, ask your financial institution to make sure their records are up to date and match exactly what you are entering as your billing information.