Blocking my postbox which was paid in Dec 2017 for 2018 year "Saxonwold"

After 3 trips to my postbox and not being able to open it, today somebody was there to tell me what was going on. The lady who came when I rand the bell said she didn't know, maybe cause I didn't pay and sent me to the post office next door. Post office says they have nothing to do and my postbox was paid on Dec. 09 2017 for 2018 and even so they could not block it. She send me back to the other, go there nobody to be found or answering my calls. Now that was at 2h30 pm working hours. Back to post office to say there is nothing they can because they don't have access, come back tomorrow...........

Really how many times must one come out of work for not sure what since I'm sorted and they are the ones who wronged me.