Query on premiums

I am so f*en angry about the bad customer service at old mutual, my mother have a funeral policy with old mutual and I am currently making the monthly payments on her behalf , the debit order started to go through my bank account in 2013,last year they increased the monthly premium without informing us, my mother wrote a letter to their office to advise that she will not afford any more increase on the monthly premiums, however old mutual responded that if they leave the premiums at a fixed rate as requested then the cover will decease manual, which is nonsense, which law in S.A insurance policies stipulates that part? Old mutual is bad news, they are ***********, I will be terminating the policy with them because I will not stand for this unprofessional behavior from their office, I WOULD LIKE TO WARN ALL MY FRIENDS AND FAMILY NOT TO USE OLD MUTUAL SERVICES