sadly if your looking for an employer that is honest and does the best it can for its staff , quit now , before you watch your life spiral down the loo working for a company that is not a good one.
this practice of taking on part time staff even when people such as yourself are on contract and want the work is common, i think however i may be wrong but you yourself are part time because of your contracted amount of hours.
so from the post offices point of view its better to have more staff on part time basis then on full time contracts as they save loads drom not paying as much holiday or sickness pay and i think there are a few othere imorall savings they make as well.
this is a techniuqe used in tourist areas as work is seasonal and business dont want to be tied to staff . so it works out for the employer but not tso much for staff who need a certain amount of hours to pay the bills and feed the family .
my suggestion is this , give th post office the same amount of respect they show you! alweays be looking for another job and do the least amount possible because they will do the same in relation to your job.
the subpostmaster before me was nearly cheated out of his retirement package after working for 30 years straight , he got ill , so they tried to in the last 2 months to make out like he was not keeping to contract and tried to withold his pension . not one thank you , not one mark of respect, he had to fight for it, even after 30 years service.
remember you are disposable , only upper management are safe,