Update: well, in the end I was able to open the statement, I did not read the message with which the statement was sent. The password goes like this: your birthday XX Day XXX month xxxx year add your last 4 digits of your mobile number registered with UOB, so that could look like: 01Feb19601234,
I went to my Bangkok Bank branch at Robinson Surin and the lady who served me was extremely helpful. She was able to put UOB again back into my BBL account.
After an initial trial payment of 10 Baht the lady asked me to do, UOB confirmed that they had received the transfer, after that I made the full transfer to UOB and that worked!
Voila, this really saved my day!