I've been having issues with my DLC because ever since I've cleared my cache my DLC hasn't been working, so I went onto XBL and redownloaded all of my DLC. However, even now, I can only access Wizards Tower and the Thieves den... What happened?

Sounds like you might be missing the patch -- what version does it show you are playing ? -- only the older DLCs will load on an unpatched game the newer ones were made with an updated version of the CS and will not load in unpatched games !