WiFi calling gets disabled automatically

Wifi calling when enabled from Settings/Cellular or Settings/Phone, gets enabled. But when i go back in settings i see that the wifi calling is disabled. Thought it says it has enabled, settings is not actually enabling wifi calling. Hence i am not able to enable use wifi calling, My service provider is Mint Mobile. According to their system, wifi calling is enabled for my account and they asked me to get in touch with Apple to solve this issue. My iphone xs is running on iOS 13. Faced same issue with iOS 12 as well.