Unlock iPhone 13

I purchased a new iPhone 13 at AT&T store and started school in the UK. I was told if I paid in full my phone would be unlocked. I got an email confirmation that my phone was unlocked however 5 days later my SIM card from Uk isn’t working. I took it to Apple Store and representative writes a report how AT&T still marks the iPhone 13 as locked. It has been 2 weeks of going back and forth with AT&T leaving me stranded in the UK with out a form of communication device. Extremely detrimental to  personal life, profession and academic responsibilities. I need this rectified immediately. I have spend  so many stressful hours and days trying to sort this issue out. AT&T fails over and over again.