I'm unable to use my network ussd code in my iPhone X

I have been unable to use my network ussd code in my iphonex it keep showing error message “error performing request unknown error” and i called my network provider customer care they assured me my line is working perfectly I don’t know what’s wrong because i can’t receive call or message for the past five days PLEASE SOMEONE SHOULD HELP ME 😭😭

[Re-Titled by Moderator]