Why the extra charges?

I recently purchased a washing machine from Makro Strubens Valley paid for the white glove service as I needed assistance setting it up. When the delivery guys came they had informed me that the connecting cable that’s needed for the washing machine is too short and it requires a longer pipe,I said oh okay cannot I just buy it from any hardware convenience store they informed me I can but because I paid for the white glove service they cannot leave until the machine is properly installed and they need to test it is working properly,they informed me that they do have the cable with them but it would cost an extra R450 as it’s a service they do not necessarily do,I asked even though I paid for the white glove service I then need to pay another R450 just for a cable?they were insistent that they cannot leave until the machine is working and that would require the cable,I reluctantly agreed to pay it as I had other errands to attend to and was growing increasingly uncomfortable with the insistent demand.