Staff give me different answers with every call I make

I was told my package would be delivered on Monday once payment was made. I made the payment on Monday morning and sent through the proof of payment to them. No delivery was made on Monday. I called them again on Tuesday, and they didn't check for my payment, so nothing was processed. They said they would process it and send it to be delivered on Tuesday. There was no delivery on Tuesday. Called them again today, on Wednesday, and they tell me that my parcel will be delivered on Thursday because the driver is fully booked. I call them back an hour later, and they tell me my parcel has not been cleared yet, and they can't promise me a delivery for Thursday. I paid the expensive option for the express delivery and this is the service I receive? How many times must I call and how long must I wait? This is extremely frustrating, as this parcel is urgent!