Can I lock or track my stolen iPhone with IMEI number?

can i lock my device or track my phone with imei ?

No. Your carrier might be able to use the IMEI, but it will take a court order for them to act.

my phone 'find my' is on but it turned off recently (not by me) how is it possible to turn off my 'find my'

Whoever has the phone cannot get into your phone at all to change anything unless the phone was not locked using a passcode. There is no way that anyone could ever guess your passcode in less than 10 tries and then change any settings on the phone.

Keep in mind that Find My is not going to work.....IF.....

1) The battery has run down

2) The phone is powered off

3) The phone does not have an Internet connection where it is currently located

There is really nothing that you can do about his except keep checking a few times to see if the status of the phone has changed.

Unfortunately, you have to be realistic about things. Only a tiny fraction of lost or stolen phones are ever recovered, so if no progress has been made after 4-5 days, the phone is gone.