having centralized wallet, where you have no access to public and private keys is a bad thing (and no they will never give you the keys, because than they loose the control and they will never make sure if the reason you lost your coins is because of you or them). Blockchains are decentralized for a reason. Hardware wallets also have their reason, put your coins on a cheap usb stick and you will regret it later.
To safely store your coins you can use a hardware wallet, or use the offline wallet on a computer which was never and will never be connected to the internet, create your keys, save it on the computuer, write it down and store it in a safe or give it to your mum, so its not in the same location like the computer its stored on.