Ridiculously high purchase charges/fees

The level of service has dropped over time and they have recently introduced ridiculously high bank charges which they charge you when the merchant banks the money reserved for purchase which is previously debited from your account and they sent an SMS as a confirmation of the transaction and there is not enough funds days later. They still are not answering why if they reserve the money when the purchase is made and they debit your account why do you still need to have the same amount days later when the merchant banks the reserved amount. Talk how ridiculous the fees are which in a way they are pushing people to have overdrafts in their accounts so when you don't have they apply this punitive system. They are happy you are in debt which means more interest for them. By the way they never had this and they are probably the only bank doing this. How sad that they are cheating people money. The only option is to start carry cash or change them.