Seeing as you have never been community-removed or perma-banned it's likely that you could chalk it up to a glitch or somehow unluckiness/accidental deletion.. I imagine Rubik can help you with this issue though -- if you're 100% sure you've bought the CC and not someone else, you should be able to get everything restored.
You should definitely prepare information for Rubik to take in such as your CC command, last CC job name and if the account you're on is the account you bought the CC on.
Normally your CC is supposed to stay forever even IF you're inactive -- only your custom content will be wiped temporarily. I came back after a 4-year break and I still had my CC so maybe you just got hit with a glitch/accidental delete.
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SwaVe's post in Custom Class was marked as the answer