Wrong parcel delivered to me, and being sent back, on my dime

Through TCG's online system I arranged collection on Friday 21 Aug of 2 parcels from a supplier, to be delivered to me. The driver collected my 2 boxes and also another customer's 4 boxes, which he incorrectly assigned to my waybill, with a hefty price tag added to my account. When they attempted to deliver the 6 boxes on Monday morning (no marking to see which 2 are mine...) I requested they be RTS. That amount was also deducted from my prepaid account and I immediately received a demand for the account that was in arrears by that time. The original R283 became R1035 by then. After receipt of a case number, and being cut off after a vague unsatisfactory answer by a call centre agent at "Customer support", with an excuse of having to be helped by another agent at another office, there is now radio silence and no resolve. Emails go unanswered, not even an acknowledgement, and calls are being sent to other agents, to whom I have to tell the whole long story, again... no resolve.