Stor-age unreasonable rental increases

I have been a tenant at the Durban City branch of Stor-age for the past 5 years. Over this time, Stor-age has and does increase rental after 3 months from a previous increase, or any other time less than 12 months after a previous increase. The increase amounts are not minor and can be anything up to 12% of the current rental amount. Stor-age is doing this because they are well-aware that tenants cannot just up and leave if they are unhappy with the service provided, and amounts to ******ion. They always mention rising costs as if that gives them the the license to ****** money from hapless tenants. Is there a body similar to an ombud that we can complain to to stop this practice?