Cell C won't active Wifi Calling on contract device with bundled Wifi minutes

Cell C sold me a Samsung S8 on a Postpaid Pinnacle 250 with bundled Wifi minutes. But they won't activate Wifi calling on the device they sold me for over a year now (even if the website list it as supported) regardless of the fact that my firmware and software is upgraded. They keep telling me "your device is not supported" even though it is the exact device which was sold on the contract with the Wifi calling minutes!