Travelstart... but will they finish?

Our flights from Durban to London return have been changed by Travelstart on numerous occasions (up to 3 days) with very little explanation. We are now in London with our return flight date being incorrect! Twice we have been told by Travelstart that there are no seats available on the dates we requested. Both times Qatar have confirmed that seats are available! I have given copies of emails from Qatar to Travelstart confirming seat availability, However Travelstart point blankly refuse to change flights to the requested dates, saying there are no seats available! Their email addresses are not being monitored (no reply emails received). There are also massive delays in replies being received. Phones just ring. The telephone communication I have had with them has been frivolous! 2 hours over 9 conversations and still this situation has not been resolved!