Bad Customer Costing me money

I called Flysafair around 13.30 today, enquiring on flight amendments. I wanted to change my flight to a new flight date , the new flights tariff was at a lower price but I wasn’t getting a refund. I am happy to pay the R300 admin fee as stipulated in the policy but I would have also appreciated a voucher on my new flight price reduction. In their policy it clearly states that if the new tariff is higher you pay the difference but there’s no mention of if the tariff is lower. Leaving the guessing game to the customer. The airline is making money from customers by charging them an admin fee and also scoring on when the tariff of the new flight is lower, nothing comes back to the customer - meaning the business benefits more than the customer and the business is “King” in this scenario. In an economy where businesses are putting customers at the forefront, making sure they give back where possible, I’m questioning if this is right what Flysafair is doing. I’m sure if customers were to be asked about flight amendments on lower tariffs they would see the unfairness of this business model. The sales consultant I spoke with understood where I was coming from but informed me that is how she was traiend. I requested to speak to the manager/supervisor and she advised that the line was busy she will give the manager/ supervisor my contacts of which I gave her my cell phone number to give me a call. I could have made so many decisions at that time while waiting for the call. The flight has since gone up initially when I was enquiring to when I checked now. The bad customer service firstly of not being called back is shocking! The time wasted means a lot of monetary decisions I could have made. So the call not coming through actually has now costed me. I would like feedback on how they will address my concern and what transpired.