Shopping experience ruined by poor Admin practices

This was the 3rd time we made an online purchase at Myrunway.co.za (previously known as RunwaySale). We bought a pair of shoes for a photo shoot and needed a tax invoice including our company details. Their website has a technical problem, which is that when you edit either the billing or the shipping details, the system automatically updates both, i.e. it does not allow for the details to be different. In light of this, we placed our order and immediately sent an email with our company details requesting the tax invoice. Eventually, we received a reply from a support representative to say: "Sadly due to the order being shipped already, we are not able to edit the address on the order invoice" - meaning that I do not have a tax invoice to present to SARS on behalf of my company. This response is unacceptable because 1) we sent an email as per their instructions ("for any queries contact us at info@...") right after the order was placed, and 2) I am pointing out an error on their part and they failed to acknowledge it. After several attempts asking them to rectify their mistake and their unwillingness to issue a tax invoice with the correct details, I am here to warn other customers about these admin issues. Myrunway: an online shopping experience must be seamless from the moment we decide to support your business, to the moment we receive our order and are happy with the product. Your lack of interest in assisting with an admin query that arises due to an issue on your part creates frustration, unnecessary loss of time, and the ultimate consequence is that we will not support you again. I would rather avoid having admin problems with your platform and have a painless process with a different supplier, instead of dealing with an unhelpful "Support Squad" member who refuses to speak to your admin department and fulfil our reasonable request.