When you say bank are you referring to your broker?
For retail shorting the margin requirements are too much to make it economically feasible.
The shorting is a myth on all pinkies.
The average investor can't or it is extremely difficult to short a penny stock - the margin requirements are just cost prohibitive. You have to have $2.50 margin per share to short a stock under $2.50.
If you want to short 500,000 shares of a stock at $0.004, you have to have $1,250,000 in your account, and 500,000 shares at $0.004 is only $2000.
The good thing is you won't get a margin call unless it gets over $2.50.
IG
It's easier to fool people than to convince them that they have been fooled