Hi Mick,
Much will depend upon the contractual terms. How long has the contract to run? Is there a term in the contract that permits them to increase their payments? Did they inform you of the change in terms?
Confronted with such an increase, I would feel inclined to stop payment altogether (I presume that you pay by Debit?) and write a letter to the CEO of the company - you can find his name and head office address very easily on the Internet - explaining that you will not resume payments until a resolution is found.
Don't let the buggers grind you down!!
George



