First of all, please make sure the most recent app update has been installed and see whether this has any impact on the styles. It's also important that you are logging in with the same MMJ account used to purchase the styles.
If the issue remains, it can usually be resolved by deleting the data and cache for the Google Play Store app itself. To do this please go to the 'Settings' on your Android device and proceed to the apps manager. Find the Google Play Store app in the list and bring up the info page for it. Here you can delete the app data and empty the app cache, then restart the Android device before opening Music Maker JAM again.
After following these steps any pack purchased under the active Google Play Store user account should now show up in the list of styles under 'My music'. If the packs are still not listed however, it could be that you simply need to wait for packs to finish downloading completely onto your device.