Prosperity ridiculous premium increase

I have an issue with Prosperity which was never resolved to my satisfaction. 

I had been paying for a policy for years and out of the blue it was increased to almost double the premium of which was too much for me whereas the cover amount was never increased.

I was then told over the telephone when enquiring and was told yhat the insurer didn't increase premiums since 2015, and that was the main reason of the increase.  I am completely not happy with this because that was their fault and if the premiums increase, so does the cover amount.  I want my cover to be reinstated to the same premium i used to pay, plus pay out for the death claim of one of the people covered on the policy who passed on. I requested to be refunded everything i paid them as premium if they can't settle my matter in a way that i will be satisfied. 

Please assist me in this long outstanding matter that stresses me