Do you have to continue going to the same wic office?

The ladies at mine weren't very nice when they found out I dried up and was exclusively formula feeding. I am supposed to go back in June to get my vouchers switched out since they had already printed them but I really don't want to go back to that specific office now :/ would I be able to walk in to another? Or will getting a note from his peditrician be better? Anyone else go through this?