Air head cashier, Unprofessional Services

Terrible, horrible experience at Totalsports Canal Walk, staff are useless at the pay point. We kindly double checked with the cashier if he has placed our till slip in our bag after our purchase and he insisted he did, only to find out when we got home he didn't. Needs trained personel at the tills, and not done air head. How do I get my proof of purchase now.