Bad customer service and lack of communication

I did an online purchase of TV unit, coffee table and headboard on the 29 November 2024, the website says that it is free delivery on purchases of R3999 or more, I made a purchase of R4075 and there was no free time option when I checked out.They delivered my order to North Riding for collection and it was supposed to be free delivery. I called the call centre to tell them about it and I spoke to Monique she says that she will talk to the IT department so that they cancel my order and make a new purchase for free delivery. I gave them a call after 7 days of purchase and they told me that they are busy with my order and Monique called me on Monday 9 December to tell me that some of my items are no longer available so I should cancel my order. I told them that I'm not cancelling I want the items I bought. The headboard that I purchased is no longer available and it was R949 and they said I should choose another one I did and it was R1249 so it's R300 difference, they said that I'm supposed to pay the difference. I don't have the money to pay for that and they delayed my order. When I ordered the stock was available. I'm expecting my order to be delivered by Friday 13 November at my place. I'm not going to pay that R300 and I'm not going to cancel my order because I bought it on Black Friday sale now everything is expensive I won't find anything with that prices . Please help