Why have SLAs?

I have been in to several branches to obtain statements for a Market Link account. The branches were either closed or I had to sit in queue for hours.

The banker in the branch was not able to assist me, but put a query through to the back office. A reference number was provided *** with a 48 hour SLA.

It is now 8 working days later and I have had no feedback.

I call the call centre every second day, holding for just short on 30 minutes, when the agent cuts me off.

I've also filed a complaint from the bank's website.

I'm extremely frustrated and terribly disappointed in the lack of service.

Please advise as to what I have to do to get some assistance.