I can't trust Luno Crypto any more

What is wrong at Luno, crypto exchange? I tried to send R474 out of my account-- Luno quoted me R1240 in fees and left me with a balance of -R787 to send out. Um, how do you send a negative balance? Is this the way you operate your exchange? I am confused as to how we are to trust you as a crypto exchange if this is how Luno operates ? As you have an ofice in Cape Town I felt reassured but As usual, all of the crypto exchanges 'don't take phone calla' only support messages with 'stock' answers.