Issues following a hack?

I need some help recovering from a hack on my website. I thought I had everything cleaned up and fixed but then saw some potential problems after I did a test transaction. I'm wondering if this is a known issue and if someone can help me figure out what to change to get rid of the problem.

First off, I'm relatively new to Zen Cart and web building in general, so when I set up my zen cart page, I missed some of the early steps like renaming my admin page. I would guess that is a big reason why my sight got hacked in the 1st place.

Anyway, I became aware of the hack when my web hosting provider (IXwebhosting) sent me a note that a hack was attempted and successful. Once I became aware of the hack I followed the instructions provided to me by IXwebhosting and then follwed the instructions from Zen Cart on securing my website and I installed all of the security patches (including renaming my admin file). Then I did a sample transaction on my own site using a credit card I rarely use just to make sure the transaction worked properly. I got the credit card statement in the mail the other day and there was a transaction on it that I didn't recognize. I called the phone number that was on the statement and the person that answered was very vague and told me that they were a "reward services" provider that I had signed up for on a website using my credit card. Well, the only website where I used that credit card was my own and I know that I don't have any reward services attached to the website, so I can only figure that this transaction is a result of the hack. I was also thinking that maybe this "reward services" provider was responsible for the hack, but I'm not really sure how all that works.

Anyway, I wanted to report this as something that should be looking into. But, I would also like some help with my site because even after all the security patches were applied, the fraudulant transaction still took place.

What do I need to do to make sure the issue with my site is resolved?

Thanks.