unsatisfied customer

i had a lay by purchase at this store in Mossel Bay Mall. I forgot about this lay by seeing that my phone was broken and did not see the sms messages from them. When my phone was back on track eventually, i saw the messages. I then went to the store to enquire if i can receive a tfg voucher for my r400 deposit, but the store manager said that she could not help me seeing that i lost my slip, i will loose that deposit. i had my id and she was able to find the lay by on their system, but she refused to give me a voucher for the r400. For me this is not expectable, seeing that other tgf stores gives you vouchers