Horrible customer care

I am writing to formally raise a complaint regarding my recent purchase and the handling of my request thereafter. I purchased two pairs of pants, selecting the same style in two different colours. Unfortunately, after completing the purchase, I realised that I had selected the incorrect size. On the same day of purchase, I immediately contacted your team to request a size change only, while keeping the original colours unchanged. I later received confirmation that the size change had been processed, which reassured me that the issue had been resolved. However, upon receiving my order, I discovered that although the size had been corrected, both pants were delivered in the same colour, which is not what I originally ordered. This change was never requested or authorised by me. When I reached out to query this, I was informed that I would need to pay for the return and refund/exchange. While I fully acknowledge that I made the initial mistake by selecting the incorrect size, I acted responsibly by notifying your team immediately and requesting assistance. The colour change was not my error, and it occurred after your team confirmed that the amendment had been made. Had I known that requesting assistance would result in an incorrect colour being supp**** and that I would then be held financially responsible I would not have proceeded with the request. It is therefore unfair for the burden of return and exchange costs to be placed on me for an error that was not mine. I kindly request that this matter be reconsidered and that a fair resolution be provided.