UNFAIR TREATMENT

Please assist me, I did communicate when I was taking over the bond from my husband that with the 150 000 that we are paying was to reduce instalment and get a lower interest rate that is fixed, to my surprise the bond amount keeps growing every month. When I took over the bond I was paying R10 400 at most, now its about 11K and I explained my circumstances. Who can I speak to regarding the fixed interest rate