Home loan interest not coming down

I have a home loan. The interest rate went down end of May, they sent me a letter and June my paymnet and interest rate went down. Then came July and they put it up again, to the same interest rate before May's cut. Now comes July interest rate cut and they bring it down, however not including the May only the July cut. Now they want to come with a story of, main account holder not meeting bank criteria and bank rebate deactivated. I have asked them to explain this, as hiw can this be They are not answering me. They are talking about 365days interest with 28, 30, 31 days, that I totally undersatnd. But they have not given my May cut of 25%. As why do I get it for one month and then they put it up again. Also does not not help you have a private banker. For everytime zi have contacted them to help me with betere rates for purchasing a vehicle or my house they did not want to help.said I my phone home loans or vehicle finace. So why am I paying extra fees for a private banker who does not assist. I have been with FNB for over 20 year. Think it is time to change banks.