Samsung Galaxy S21 FE 5G Won't Show 5G Option in Network Settings

I purchased a Samsung Galaxy S21 FE 5G smartphone from Teknosa. Despite the device supporting 5G, I'm unable to use 5G on my Türk Telekom line. Even though I have a postpaid plan and a 5G-compatible SIM card, the 5G option simply doesn't appear anywhere in the phone's SIM settings.My carrier says I won't be able to use 5G because the issue is on their end — but my phone's model name clearly says "5G" right on it. Despite that, the fact that the device's network settings don't offer any 5G option at all has left me both frustrated and feeling like I've been misled.I'm asking Samsung to remove any software-level or other barriers blocking the 5G option on my Galaxy S21 FE 5G, activate it, and carry out whatever investigation and adjustments are needed so that I can use 5G on my phone without any issues.