Ask HN: Should I sign my new job contract prior to my interview trip refund?

So I did a trip to another country for taking an interview. Prior booking my tickets the company (which has around 500 employees) promised that they would pay for my trip. I did well in the interview and they offered me the position. At the end of the interview they gave me a paper, that I had to fill out with my IBAN and my total traveling costs. This happened 12 days ago and I until now I got no news regarding that matter. In the meantime they sent me my work contract.

I have no prior experience on how these situations are handled and how much time a refund would on average need. My biggest concern is that in case they don't refund my traveling costs they would not have kept their word. In turn signing a contract with a company that does not keep its word seems like a red flag for future issues.

How should I handle the situation? Should I wait until they completed the refund and not sign the contract? Should I ask them? Should I be open with them regarding my concern?