I can't activate my 'Internet Security Unlimited' because my key is 'invalid'

I bought an AVG product from my local store and put in my activation code thinking that my current AVG had already expired. I got a message telling me that it didn't expire until today, and when I tried to activate my code for the new product, it told me that my activation key wasn't valid. I likely have no way of getting my money back on this store bought product because I no longer have the receipt and it's been more than two months since I purchased it. Is there anything else I can do about this besides forking over more money to buy another product?

Hello Ronni,

Let us check the status of the code and then assist further on this matter.
We have sent an email for you to provide the code that you bought for AVG.
Awaiting your reply!