Whats the big deal about sending a new expriy date? I presume you had setup a direct debit to your credit card for your hosting.
Digiweb can have the credit card transaction authorised without an expiry date. Did you know that if your cc has expired and your account is closed, any direct debit will be honoured by your credit card company and you will be sent a bill (which you are legally obliged to pay)?

And as for the Data Protection Act, it only covers certain types of information, you should know that. A credit card expiry date is most definitely not regarded as protected information under the Data Protection Act (age, gender, sexual orientation, race, membership of the travelling community, religion, political ideology).

If you want to make a complaint, contact your credit card issuer. They will then make a complaint to Digiwebs CC processor, who will sort out Digiweb, in a top down fashion.