Then speak to your Bank, specifically, to find out how the payment was authorised. Bacs, Direct Debit, whatever, each leaves its own Audit trail.
Having found that out, you ask the Bank to take it up with PCW, who may have, what appears to them to be, a perfectly normal set of Documents. Possibly made out by someone else. If Fraud is involved, then your bank should be able to advise you and will probably act on your behalf.