
Hi! Sorry to hear that you have this situation, could you please let me know where did you made this purchase?
Did you redeemed before losing it? If the subscription was activated before, you may not even need the 25 character key anymore, everything may already be linked to your Microsoft account.
If the purchase was with a non partner reseller, Since Microsoft has no record of transactions with non-partner resellers, they are unable to help. Maybe, the reseller may have your purchase info in their own records, if the code isn’t redeemed yet, try redeeming it; if it’s already redeemed, it will be lost as cant be transferred.
You should always avoid using third party resellers as this is against Microsoft TOS.