Store front cannot be changed

Hello, I moved from Sri Lanka to the UK last November and I changed my region to the UK store but when I tried to download a UK only valid app (Natwest banking) it asks me to change the region back to the Sri Lankan store since my Apple ID is not valid in the UK. I know if I change back to the UK store, I will not get the app to download anyway but I tried to change this back to Sri Lanka since my Apple Music subscription is also stopped currently. But now when I’m trying to change it back, it says storefront cannot be changed at the moment.

Could you please help me on how to sort this out? I really need Apple Music and need to change the store back to the Sri Lankan one. Thank you!