Late 2015 I created a BTC wallet using blockchain.info (now blockchain.com)
I sent approx. 0.3. BTC to this wallet. All fine.
Backed up the seed and made a walet.aes.json file and backed that up too.
it's pre-2016, so it's a legacy blockchain.info wallet account just like
Potato Chips mentioned
any chance you remember the address you used to send or receive that amount?
check your email, exchange account and etc even a txid could shed some light, so that you can trace and check its balance on block explorer
However, NO funds are shown and NO activity at all. I am pretty sure I didnt import addresses in my wallet, I just bought some BTC and send it to my wallet.
if indeed the 0.3 BTC transaction was made and received/confirmed, then all you need is in that walet.aes.json file
just shooting in the dark, it could be a simple uncompressed/compressed private key problem
I've seen this before when bc.info wallet is displaying a compressed key for an uncompressed (legacy) address