Hey agallag2017,
It's strange that you'd need to go purchase Hidden Springs again to access it since you've purchased it three times and should own the DLC. Generally speaking, if Hidden Springs appears in your Purchase History page on the Sims 3 Store, you should be able to download it from there.
Please contact our live support team so they can work with you to see if there's anything account or payment-related that's been triggering this. Unfortunately, we don't have the tools to investigate here on the forums, but it'd be worth having an advisor take a look to prevent this moving forward.
Let us know how it goes, thanks!