Forced shopper bag

Today I went to Woolworths Atteridgeville to get some essentials. The cashier then notified me that there were no plastics and only shopper bags available. The lowest shopper bag cost over R40,and I couldn't return what i had bought becausw I really needed those things. How can a store run out of plastic bags and make customers suffer for it by paying about R50 extra just for a bag to carry their groceries when i could've just spent about R2 for that. That is bad customer service