Moving the goal posts

I joined Medihelp in 2010 on a hospital plan. At the time the hospital plan covered everything I needed. 8 months ago I submitted a request for a knee replacement. This was declined. I queried it and was informed that they had a policy change a year or so previously. They no longer approve knee transfers for wear & Tear.. I ask you how ridiculous is that.. I asked for proof that they informed me of this change, still waiting. Don't believe at any time my premium went down as a result of the "downgrade" I signed up for a product, how can you at any time change the content of my agreement. Like me buying a BMW and halfway through the agreement they take it away and give me a mini... for the same instalment. I requested to talk with someone regarding this. That too was declined..