I’m sure by now you’re probably tired of hearing this, but sometimes artists do get uuuuuber busy with commissions. My best friend is a full time free-lance artist and she barely has any personal time to herself. She gets commissions stacked on top of each other, so sometimes orders take a while to get through since she goes down the list in the order that the commission has been placed. It may be beneficial to ask if they have an order-tracker or a slots list, just to give you an idea of where you sit.
A simple bump should suffice, if the wait time is bothering you or they won’t have it to you in a desirable amount of time, you should definitely pursue asking for a refund. I buy quite a bit of art and sometimes wait times have been really long, as in like, 3 months for it to be delivered. The best advice I can offer is to keep a clear line of communication, not in a rushy way, but as a concerned customer type!