elbarto, please ring the call center even if you can't find the receipts. Ask to be put through to a supervisor or to have a supervisor call you back. I have spoken directly to supervisors before and given them dates of specific purchases. They have the ability to look up individual transactions just based on the date of the transaction and the store you went to.
With the Woolworths bonus offer, was the purchase over $30? If it was there would hopefully be a fuel voucher generated from that visit. If that voucher is there then that gives at least some proof of the transaction. It might take some work on the phone to get through to someone who can understand the situation, but please be patient and persistent. Good luck.