how can i remove find my phone when my phone is switched off.

I have sent my phone to Apple for repair but forgot to remove find my phone. My insurers have now contacted me to ask that I do this so that the repairs can be carried out. I have tried to do this on my computer, without success so phoned my insurers who told me to contact apple support who should be able to remove this by remote access. But apple want £25.00 before they will provide technical support. Can anyone help please?