It is fair. Nobody asked you to continue doing it or to keep the extra items you gained from doing so. Judging from how many items in your inventory were duplicated, you should’ve been well aware of what was happening.
Can you read the rules and quote the rule(s) you broke? If you do not know how to quote the rules, read the guide How to quote the rules.
If you do not identify the right rule(s) that you broke or you do not know which ones you broke, I can make it clear.