Iphone screen is compeletly blank. Trying to restore it on itunes and the phone is unable to be factory reset.

Try these two options before arranging a repair

Frozen phone

see the process below, using the Update option if possible.

Work all through it. There are several stages.

If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support

There is no guarantee you can save any data since your last backup if you need to use the Restore option.

Recovery mode or DFU

 https://support.apple.com/en-gb/HT201263

Arrange a repair

https://support.apple.com/iphone/repair/service

or: contact Apple Support 

Anything other than Screen or Battery may be a replacement phone and the price is in the article.

You can see additional service information within the following article:

Prepare your iPhone for packing and shipping