Used them for an hp agreement for a car purchase, ...

Used them for an hp agreement for a car purchase, wrong direct debit details set up, told i could change after first payment, after first will not allow me to change, do not answer the phones, do not reply to emails. I have had to cancel the direct debit to try and get a reply!
Strongly advise against using this company as they have zero customer service and are proving ultra difficult to communicate with.