Did you write yourselves into a corner that said you'd demand all suppliers to be ISO 9001:XX certified? If so, what are your reasons? The actual standard does not require this, but maybe you have a good reason for it.
If they are a critical supplier, you're going to have to change YOUR requirements, if you want to keep this supplier. If they are not critical, and there are replacements out there, just drop them.
What other things do you do to qualify and then keep control over your suppliers besides the ISO requirements? As an example, we DO ask suppliers to maintain ISO certification, if they can, or maintain a QMS. But, some of our critical suppliers are small enterprises, so we qualify by visiting them and assessing their operation, have them fill out a survey detailing their operations for us, get samples and run limited production trials, ask for process QC records, and, to avoid risk of poor material getting into our production, run receiving QC on receipts.