Why am I not accumulating vacation hours?

Ask the manager or HR.

No, we don't have any idea why. You are going to have to ask your HR department--they are the ones who make your rules. We have no idea what those might be. 

How long has it been?  You are likely to compile one or two weeks per year, at most.

Okay, so many companies offer one week vacation after a year of work. An average of 2000 hours fulltime earns 40 hours of vacation.  At that rate, 50 hours of work earns you on hour of vacation. It sounds like you only work part-time. I'm amazed that they allowed this at all.

Maybe when you took more time off than a full-time employee was entitled to they switched you to part-time.   

It's reasonable to expect that if you want the benefits associated with working full-time that you actually work full-time.    I personally find it odd that they paid you for vacation time you hadn't earned. 

You'll need to ask your employer.

Sounds like a question for your manager.

Ask your manager. Don't ask random strangers on the internet.

You need to ask about accrual rates and policy. Then, if you don't understand, ask your questions.

Hmmm, ask your boss or ask total strangers 99.9% who have never worked there. Which do you think might be best?

No one on here could possibly tell you why. We don't know where you live, what the store policies are like, how vacation hours are accrued, nothing. This is something you need to discuss with your boss, not a bunch of strangers online.