Cannot use wifi calling on Go-phone

Why can I not use wifi calling on my iPhone under the GoPhone plan? No one has explained to me yet as to why that option is not allowed for prepaid customers. I bought my phone outright and yet I'm being denied the ability to use certain features for some stupid reason. I already can't get my phone unlocked until I've been in jail with this company for six long months. So why can I not use the wifi calling feature???