More stuck than superglue - UK Freelancer - US Tax

Hi please could someone advise?
I'm a UK freelancer who has provided a freelance service (and image licences) to a US based company.
Not sure if this is relevant but will mention: I have a English registered LTD company and operated through my trading name (making the LTD details clear too).

What form/s do I need to fill in? I've been asked by the client to fill in and return an i-9 form but I believe this to be incorrect (think this is for non US employees to prove eligibility to work in the US).

What form should a LTD company freelancing for US company fill out? W8-BEN?
I'm reading 30% tax might be deducted... I'm hoping that isn't the case!!!! I've worked myself to the bone for this job.
Can anyone unstick me?

Thanks!!