Beware of Standard bank *****

I bought a home through Standard bank home loans 11 years ago, afte about 8 years of paying for my bond I found out through one of their statements that they had increased my boy repayment period from 20 years as agreed on our contract to 30 years. This was done without mu consent and they never even bothered to inform of this. I have been calling Standard bank call center for about 3 years now begging them to change back to our original agreement but they just tell me they will call me back or they will change it or I must write an email asking them to change it back but 3 years later still nothing has changed. I have even tried to go to their head office in Johannesburg and was told there was no one who could physically see and help me as their homeloan doesn't have a walk in facility. I am now paying for my home for an extra 10 years I never signed up for as standard bank seems it fit to take me for a ride and then become unavailable. I have asked them over and over again if this is legal because I am not a law expert but it feels like ***** to me.