How to Respond to Order Fulfilment? Automotive Superstore

I put through an order with Automotive Superstore for a head unit replacement kit for my car. This was on 7th May. When ordering they provided great support and walked me through the parts I would need. They initially advised it would take around 2 weeks to fulfil the order, which I was fine with.

On the 21st (2 weeks later) they advised it would be an additional 2 week wait for the head unit to be in stock, and offered me a upgraded head unit for a discounted price ($60). I didn't particularly like the new head unit, but accepted as I was excited to get it installed.

I received the package on 25 May, had the following issues

• One of the items (a wiring harness) was left off the order so I am unable to install the head unit
• The upgraded head unit is not compatible with the rear camera I ordered, so I need another connector
• An additional item is required (an aerial connector) that I was not advised about
• They included an additional product I did not order

I immediately emailed them and requested the additional parts they omitted. Finally on the 3rd July, they sent me an email saying they were sending me an adaptor for the camera, ignoring my main issue which is the wiring harness.

They are impossible to contact via phone, email only for communication.

At this stage it is a month since my initial order, and 2 weeks since I received the incomplete package. I would like to return the upgraded head unit as I really do prefer the original, and only accepted the upgrade so it could be installed faster.

Whats the ozbargain take on this, am I entitled to revert to the original head unit as they have been unreasonably slow, or am I stuck with the 'upgrade' as I agreed to it?

Update - I finally got through to them on online chat (took literally 5 hours), apparently I had the part I needed, but it was bundled with a different product to that indicated on the website. Given this is my main issue I will proceed with the install, and they are sending out the additional cable now. Overall they are great to deal with when you can contact them, it's just way too difficult to get onto them