Standardbank Bond instalment increase with a decrease in Repo rate.

Good day, The repo rate has decreased, however my home loan instalment has increased by +R450 per month. I have contacted the home loan department, the lady was extremely rude, and advised there is no error, but could not explain on why the instalment increased. I have contacted the prestige banking team, they advised a 3 day turnaround period on email, yet when I called the called telephonically yesterday the lady advise she will provide feedback by yesterday afternoon. The service is extremely poor and sadly no one can explain the increase. According to all financial indicators, a decrease in repo rate should see a decrease in bond instalment if the rate is linked to prime. So why is it different for standard bank?