Delivery fees!!

A couple of months ago i noticed that i was being charged for deliveries. I have a subscription for deliveries. When i queried it they told me i had cancelled my subscription. I had definitely not cancelled it as i use it usually twice a week. I didnt feel like an argument so i let it go. My latest order request was for R357.92 so as it was over R350 i went ahead. When the final invoice came through it showed a delivery fee of R36. When i queried this i was told thst my order never reached R350. When i looked again at my invoice i saw that there was an amount of R91.57 in my wallet which they app****. I didnt know there was any amount in my wallet. This then brought my amount down to R302.35. So they charged me a delivery fee in spite of the fact that my order was for R357.92. I should not be penalised because i had money in my wallet. I have since sent two more emails to them requesting a response. Nothing, zilch, nix, zero response. I am very unhappy and am now tempted to close this account and use my free delivery pick 'n pay account instead.