Time Capsule is not backing up in Time Machine.

I bought a Time Capsule from the Apple Store online that was not new. It has had repeated problems with not backing up my iMac in Time Machine. Because I was not aware of this, I have not been reporting this problem prior to October 2017. AppleCare keeps saying "Let's watch it and see how it is backing up." One senior advisor said there was not a folder that would tell me the times of the Time Capsule backups. Recently I spoke with a senior advisor who knew how to find that folder, and he was able to confirm that the Time Capsule is not backing up every other hour as it should. I also have a Seagate external hard drive that is backing up usually appropriately. In system preferences Time Machine indicates that a backup will be performed every hour for 24 hours. If this is what is supposed to occur, then because I have two places to backup, it should alternate between the two devices. In other words the backup should appear on each device every other hour. This does NOT occur. I'm worried it's because the Time Capsule was not a new device bought online from apple.com/store. Any suggestions about what I should do? I want redundancy in backups. I'm not comfortable with only one place to look for a backup. Recently an error occurred with the Time Capsule and it didn't backup for 10 days, and Time Machine took those 10 days before it announced to me that a backup wasn't occurring. When I was forced to do a wipe of my iMac and a reinstall of the operating system of High Sierra, I was unable to access any of the Time Capsule backups and was forced to use an older version on the Seagate. Any information would be appreciated. Thank you.