Blocking Account for a small amount

My Credit Card was block for R137 from the FNB ***** Department, unnecessarily. I could also not transfer money into the account due to the blocking so that there is funds for the budget that went off. <br> What I cannot understand that FNB does not stop the =account for large amounts but block my account for small amount.<br> I am checking my accounts and its my responsibility, I did not ask FNB to stop or block my account for any small amounts, this block create a massive problem for me, as this was assurance for a plane ticket in London.<br> <br> I have already cancelled my Cheque card and I will soon cancel my Credit card....I d not need this