Disgusting overcharge by Courier Guy

I sent a parcel overnight from PMB to JHB Takealot. Dimensions were incorrect. I was told to pay R184 extra. The service will no longer be overnight. I want the service downgraded to regular service as the parcel will no longer reach Takealot overnight. Courier guy refuse saying that it reached JHB overnight. All parcels from pmb regular and overnight reach JHB overnight so this is an invalid argument. Courier guy has made me pay R184 extra for a service they cant deliver. That is downright theft. Disgusted as i have used them for years (weekly). The agent and his manager are downright arrogant. Parcel T87F3B