Getting new mail/parcels before older ones

Title says it all. I’ve bought a few things, like around Boxing Day and even last week, and I’ve received them promptly. However, the items I purchased back in November are still missing. The thing is, they’re not in a package that needed to be scanned; they’re regular paper mail items. So, I have no way of knowing where they are because there’s no tracking information. Is anyone else experiencing a similar issue? Luckily, the company I bought it through already gave me a refund for it but still…. I’d like to know if I’ll ever receive them.