Postmates is a shady, rip-off outfit that thrives on and exploits ambiguity. They are deliberately hard to reach. You may believe you are ordering "delivery" but will be bait and switched into "pick-up". If you try to cancel, be prepared for an arduous, lengthy, bank-involved, fraud dept involved odyssey designed to take your money and wear you down until you give up - like an insurance company.
There is a reason this site has a one star rating in aggregate. Consider yourself warned.