I had recently booked a ticket using their online portal. I tried using VISA twice, but it showed transaction failed. Then I booked using SOFORT(successful). Next day I found they had credited the amount from the VISA transaction. I sent them a mail (it's been 2 days no response). I then tried calling them, each time they forward me to their english customer desk(As my German language is poor). I've waited for 45mins, 1:30mins and presently 30 mins. They are not responding to anything. What should I do
In a situation like this (and if you're sure the money was charged and not just "blocked"), if all attempts to resolve the issue with the seller (Deutsche Bahn) fail, you can open an official dispute with your credit card provider.
Please check with your credit card issuer - every bank's/issuer's process is slightly different. You will be asked to provide a description of the incident and your proof - you should explain that you were double-charged, you should say that multiple attempts (in writing) to reach the seller have failed, and you should send any proof you have (something that proves your SOFORT transaction went through, your actual booking, etc, ideally with both showing the same amount that was charged to your Visa).
I have successfully used the credit card dispute process in the past to dispute a double charge for a car rental, an invalid airfare charge where the airline was clearly wrong but wasn't responding to contact attempts, etc.
The English support hotline can be a pain sometimes, and it costs money (luckily per call, not per minute). If you have a coworker or friend who speaks German, ask them to call the German hotline for you, and only do the validation of your personal details yourself.
In general at the moment, especially during the aftermath of the storms on the 28th and 29th of October, it's possible that they are really backlogged and simply have not managed to get to your email yet. Usually they do.