Unfair Refund policy

My daughter wanted a cellphone, she had R600 so she asked my mom to help her lay-by since she is under age. I later decided to buy her a cellphone at Woolworths. I asked my mom to cancel the lay-by since their policy States that the lay-by maybe cancelled at anytime with full refund. My mom went to cancel but the store manager says the store policy is for her to pay in full before she cancels or else take something else from the store