Uncertain recruitment process

I had been invited to an interview. I attended the interview, two hours later I get a call regretting me. Than two days after the interview I get another call saying I am successful. I am so excited I ask for a dummy payslip. A week after I have accepted the position,awaiting some feedback from head office, I am told that the position that I had been successful for has been sourced internally. I had already resigned based on the payslip I had received. I have emails to back this information up. I am in the human resource function and this this the most unprofessional company I have even dealt with.