Horrific experience for old-aged couple

My wife and I bought tickets via a travel agent. We connected with KLM from London Heathrow, but as we required wheelchair assistance we arrived at boarding gate only after it closed. KLM refused us boarding and forced us to buy new tickets to continue the journey. I tried to claim this from KLM with absolutely no success. During this process an error occured and my flight return was cancelled while my wife's booking remained intact. After days of struggling with KLM on email, Twitter and facebook and eventually directly calling KLM in Amsterdam, my booking was restored. (I spoke to Mirjam in Amsterdam). I printed toe eticket after my booking and reservation reappeared. Today when trying to book my seats, I discovered that it once again disappeared. As an elderly person I have already wasted so much time, energy and nerves on this issue. i am bitterly disappointed in KLM and even now I am not sure how it is possible that my reservation once again simply disappeared!!