Exchanges, at least the centralized ones, aren't going to give you 12 word seeds. Mostly only non-custodial[1] wallets do.
Also, your bitcoin being "unhackable" even if it's only on a USB drive completely depends on how you set it up in the first place. You might have done the backup on a malware/virus-infected computer, and your seed might have been exposed.
[1]
https://cryptosec.info/cryptocurrency-wallets/#noncustodialThose guys just do not like my Bitcoin price predictions, so calling me a troll makes them feel better. I think price is going much lower, but it is volatile and there is a lot of money to be made on Bitcoins price swings.
I have no malware or viruses, How do I use these seed words to get back Bitcoins that were on a USB drive ?? How in the world would anyone or anything know how many bitcoins I had on a non connected memory device ???