I've been a customer of Postbank for well over 10 years. The worst thing about Postbank for me is the so-called telephone banking. All you get is someone with no idea of customer service giving you one 'leider' after another (leider is the German word for unfortunately, it also appears to be German for sod you). They should check out the service that First Direct has been offering in the UK for well over 25 years. THAT is telephone banking. Postbank are way behind the times.

A start in the right direction would be:
1. Customer service training.
2. Study what First Direct are doing. Learn from it.