If you can't find any service center willing to do this, don't be afraid to repair it yourself, it's not that hard. I have replaced the battery of a ZF3, there are videos on youtube showing how to open it with a heat gun (you can also use a hair drier instead) and disassemble them. (small tip, when you remove the screws attach them to a magnet so that you don't lose them).
What I'm not sure is where you'll get the replacement button for it. Maybe you can check on ebay, there are people whose phones broke and sell them very cheap for those like you who need spare components.
