One SMS will not be deleted from the email application

I have a phone (HUAWEI Y6 2018) that has recently received a text message purporting to come from a postal company (AusPost). However, the subject of the message simply says "(No subject)" and when I try to open the message, it just does not open. With that in mind, I tried to delete the text, but only to not delete it and stay on the page. I have tried several things to delete this text, such as:

  • Erasing data and cache for the email application
  • Trying to locate the folder where messages are stored (I can not find it)
  • Download applications such as Handcent and Backup & Restore to use their SMS removal features
  • Install the latest system update and try again
  • Adding a contact called "AusPost" and deleting the message

All does not prevail … the SMS seems to be stuck in the inbox.
So what am I doing now? I do not want to root my phone and I want this message to be gone.