Home loan and house finance complaint - FNB are like skilled ******* and ***** stars who ***** your money without you knowing

For the past 7years FNB has capitalized the calculated interest on my home loan on the last day of the month while we had an agreement that they will debit my account on the 20th of every month. They were supposed to capitalize the interest on the same day of my dabit order. This has being happening for the past 7years. I have complained more than 4 times now with them and nothing is happening. The last complat was on the 7th/08/2020 and I was promised 7day resolution but still they are failing. Instate of fixing their problem they keep inconveniencing me. The changed my debit order date to the last day of the month without my knowledge and authority to cover up their mistake. Today they have double debited my account. All this happens after I decided to move my bond from FNB because of their continues failure to give good service and disregard of their customers. I am paying more with almost r2000 on my bond yet there the balance stays the same or moves just a little because off their mistake of not aligning the interest capitalization day with the debit order day as agreed. I suspect FNB owes me a lot of many and they want to run away with it as I am leaving them. I want the most senior manager in Home loans and house finance to urgently resolve this and call me.