My iPhone suddenly started showing me an activation error

I am new here so please forgive me if it's the wrong place to ask. My iPhone suddenly showed me an Activation Error with the message "Activation could not be completed. Please restore the phone and install the latest version of IOS and attempt activation again. If the problem persists, please contact customer support." - when I googled it, some solutions would say I need to download the OS from a laptop. But I do not have a laptop, this iPhone and another phone are all I have. Please tell me what to do, I need to access my iPhone urgently. Thank you