I am locked out of my itune app store how do I get back in please help me what did I do wrong ???

Please help me to enter my app store account I got my tom and wanted to pay with the app card I had purchased which I paid $50., and had or have $43.58 about and cannot re-enter my account couldn't pay with the money stored in my app account that I may haave made a a mitake somewhere...I was beeing asked to pay with a visa card and I refused because of the amount that I hade left in the account.....can you help me.

I am an elderly Great grandmother of 83yrs old and have a hard time usning these high tec things but love them. It keeps me alert playing those games.

thankyou

Irene Dugas