someone on blockchain support ask me to tell him my back up fund 12 word in order to reverse my bitcoin which was unconfirmed in my transaction
Sorry to say, you were definitely scammed.
You cannot reverse a bitcoin transaction in that way, the scammer only told you that so that you would give them the 12 word phrase. With that phrase, the scammer could ...
Blockchain.com is not a blockchain node, it is an explorer. They have no constraint on following the same rules as a Bitcoin Core node, and can keep orphaned and forked blocks available if they wish to, and return all blocks they know of for a block height if they wish to.
In the main Bitcoin chain, things are as you say - Only a single block may survive at ...
Blockchain.info (and other block explorers) do additional processing of the transaction data in order to make it more user friendly to follow the path of coin movement through multiple transactions. Additionally, it seems that whatever you are using to print out the transaction details is not showing you all of the information.
In a transaction, each input ...
By design, it is not possible to determine the private key for arbitrary addresses.
If you do not have a wallet file, seed phrase, or other form of keys that lead to that address, no one can help you.
If someone asked you to transfer Bitcoin to a watch only address claiming it will be accessible by you, you have been scammed.