Interest rate

Good day. I've tried really nicely to liase with your consultants via email regarding a request to have the interest rate lowered on my car finance and each time I've received a different answer. The first consultant wrote to me and said "Unfortunately we are unable to assist as interest rates are negotiated prior to the contract being signed. It is therefore not reviewable and remains in force for the duration of the contract." After complaining about this, a second consultant then emailed me and said "Unfortunately, we are unable to review the rate further on the above mentioned account as we assisted with a rate review last year." If this is the case, then why did MFC give me a rate drop of 1% in April 2017 and another in April 2018? Furthermore, I've been a good client and paid my instalments on time for the past 4 years - is what I'm asking so unreasonable?