Refuse to pay as agreed

The company offered a job to do wellness testing for their client Bankmed retired employees. The job was done on a door to door basis. She agreed to pay R200 per day for travelling plus per case. After the first day I told her it was an expensive job for me and requested if I can return her bag, she agreed though when I went to her office the next day she convinced me she will give a better rate R600 for the work done the previous day. She then asked me to do two clients at Eldoradopark . I did then she became quiet and I looked for a part time at a Hospital. She then called to ask if I could bring her bag I told her I was working and knocking off late and I asked her if I can drop off the bag at Leratong Hospital and she agreed. She paid me R586 all in all saying she pays R2 p/km and she paid for one person at Eldoradopark. I dont know how did she calculate my km travelled for the Soweto day I did. Nurses must be aware of this company because it is all about loyalty.