Credit History is held by 3 companies. As mentioned, bank balances don't have a lot to do with it if you're going off the report alone, which most companies do.
If you've been rejected, your credit history is evidently not in good standing for some reason and this has absolutely nothing to do with snap. Its increasingly common for service and utility companies to run credit checks, and if you fail a credit check unexpectedly you should be requesting a copy with each of the 3 companies immediately and auditing your credit history. Evidently someone has put a mark against your name.
https://www.sorted.org.nz/a-z-guides/your-credit-history#s3.
The refund is likely a matter of process as someone mentioned, likely them putting them all through in batches each month. They will gain next to nothing by holding your money for that time period.