You ought to congratulate yourself on dodging a bullet. A chronic problem with Apple's NAS technology is its reliance on the so-called sparsebundle, a kind of outer wrapper that embraces all the goodies stored within. Based on personal experience and my reading on the web, The the sparsebundle is too easily liable to corruption (and as far as I know Apple has never taken any steps to address this issue, but somebody please correct me if I'm wrong), and there's no commercially available software tool for repairing it. Until I saw your second post I automatically assumed this was your problem, it's that common.
If you go out on the web you'll discover that some Terminal jockeys report having found solutions to this problem (although they seem to disagree among themselves about what these solutions are). If you aren't a Terminal jock and don't want to become one, then i. m. h. o. you are living on borrowed time, sooner or later you are liable to get screwed and lose all your precious data, and ought to walk away from this vulnerable technology a. s. a. p. If you are doing solo backups rather than backing up multiple Macs to a shared device, and are only interested a wireless solution, a far safer option is to pick up an Airport Extreme (they're still easily available) or Time Capsule and use a standard external hard drive via a USB connection.
NOTE: Apple's NAS technology backs up sparsebundles to a server, not a hard drive. You need to be careful here because some servers (such as the very popular Western Digital MyCloud) are often advertised simply as "drives" -- even on its website WD does not explicity identify it as a server -- so an unwary purchaser might not be conscious that he's sailing into dangerous waters.