How to cancel an invoice with validated tax lines

 I am trying to cancel an invoice but it does not let me as the invoice has already been validated.

Status is Needs revalidation.

I have reversed the line distributions but I cannot reverse the tax lines. Reverse button is greyed out in the invoice distributions.

System does not seem to let me do anything with this invoice as the tax has alreasy been automtically calcualated.

Anybody experienced a similat issue?

Thanks