Luno is a centralised exchange. This means you never really owned any of your coins deposited into their web wallet. They store the private keys, not you. You can't export them either. If you need proof, you can check your deposit address on blockchain, it's probably all gone from that address.

Only Luno support can help you. Contact them through a support ticket, give a detailed explanation of what happened along with account details, and request assistance. They should get back to you.