Can I pay to upgrade my faulty iPhone XR to an 11, instead of like with like?

I bought my XR on 22 August 19, andfrom the start it had freezing issues, which required a restart, often daily. It further has audio issues and some calls are very distorted.!

The store twice told me that the freezing is a known issues (found on website) and will be solved with the next IOS update. It didn’t and eventually they accepted to send my phone abroad for inspection. After nearly 2 weeks, it came back with ‘No fault found’.

The problem persisted and this time I took a video of it freezing and went back to the store. This time they offered a free replacement phone (after they take my phone for 3 days), like with like.

Since I bought my phone just a couple of weeks before the iPhone 11 came out,, and for just €40 less, I asked if I can pay extra to upgrade to an 11. They said in that store it’s not possible here in Malta, but may be possible in other countries.

As I am visiting Dubai in UAE over Christmas, I was hoping to get the 11 there, but cannot contact their Support from here.

I am hoping that someone can indicate to me whether this paid upgrade is possible, and how I can email Dubai Support ahead of my visit, to facilitate matters.

Thanks for your valued advice.