Disingenuous Dealings from Standard Bank Home Loan

I have been a long standing client of Standard Bank with two active and up to date home loans. We contacted Standard Bank in March as we were offered a better rate to transfer our home loan to another bank. 19 March , Standard Bank rates division confirmed via email that they would give us a 0.5 interest rate reduction if I transferred the debit order to come off a standard bank account. We accepted the offer and I transferred the debit order on the same day. Standard Bank effected the debit order change and has defaulted on their offer. They offered it in writing on 19 March ! We have since been contacted by about 4 different people saying the best they are now willing to offer is a 0.25 % reduction and , in addition, they didnt apply any reduction and took the full bond payment off. Disappointed, Shocked and appalled at the tactics employed.