Port 53 denying Clamav update

I run SuSE 9.1 on a standalone workstation with Clamav as a virus checker. Clamav worked well until recently when for no apparent reason I was unable to obtain daily updates with "freshclam". There has been considerable correspondence about this on the clamav users forum without a positive result but experts there think that either my SuSE firewall or my ISP is preventing both UDP and TCP packets through my port 53. I am no expert but I am inclined to agree with the former. "nmap" only shows ports 22, 25, 111 and 631 open to TCP and I am unable to telnet to loclhost via port 53. If this is the case, can anyone tell me (in simple terms for a newbie) how I can open up port 53? Thanks, Gervase