Useless Share Trading Service

I have sent two emails (April & May 2015) to FNB Share investing with no success. One guy did promise to return my call but never did. I bought 162 shares in a company called ASSORE LTD to the value of R56099.94 . I have traded additional shares in the same company many times but never sold out my original 162 shares. Everytime I make a sale the online platform reduces the cost of purchase of my original 162 shares. Now my June 2015 statement reflects the cost price of 162 shares as R17 835. How is this possible that the cost price can change? I hope that FNB is not reflecting the gains incorrectly on my Tax certificate which is a serious concern. I have such low confidence in the share investing platform that I am concerned my old Tax certificates are incorrect. Can FNB please explain the variation in writing to me? The monthly fee I pay is not worth it if FNB cant deliver a professional service for share trading.