Blocking or deleting a sent message Please advise urgently on my below problem?
I sent a message to a contact in error at 16:11. Apon realising this i noticed only 1 tick next to the messages. I then blocked the person,switched off my data,switched of my device, took out my sim and even uninstalled watsapp. 
How will i know whether the person has read the message or not?
If the message shows one tick in Whatsapp then it is already too late. The contact will receive your message when they open their Whatsapp app on their device.

If you had turned on airplane mode whilst the clock timer was visible on the message then the message wouldn't have been sent, and you could have deleted it to prevent it from leaving your device.