keep trying other banks in other areas' one will open an account for you, other way is to use an agent
regarding yearly 'married' extensions, if going back to UK, you should legalize the marraige cert there , as posted by ubonjoe, it's a long winded process
if you need to extend your permission to stay here you can do a 60 day visit Thai wife extension without the legalization paperwork, one extension per entry into Thailand,
if you need longer then a multi entry non imm visa from Savannakhet is i believe possible with a non-Thai marriage cert,