Standard Bank Merchant - Te450 Rejections issues

I have been registered with Standard Bank Merchant since 2014 and had few problems since mid 2019. All of a sudden I received emails referring to Rejections Te450. In the beginning were the issues resolved by the bank but late last year everything changed from their side. For once I make use of Standard Bank Merchant to provide my business with a secure card service. According to me Standard Bank should protect the customer from suffering any losses due to these Te450 Transactions rejected from the moment the card has been swiped. Now I was told to pursue the Banks to obtain a letter which I in return have to submit to Standard Bank. Nedbank I phoned twice and every time they said they will email me the letter bur never received it, secondly First Auto just said they will not be able to help me as it is a Standard Bank issue. These emails were forwarded to Standard Bank with not even a response since the 10 December 2019. What has changed and why has it become a client issue to resolve as I do pay for a service not rendered by Standard Bank Merchant?