Any idea how to refresh Proxy DNS entry

One of our customer site change its ISP, So web page use new ip
address. From our BM 3.8 I found site (www.york.ca) still pointing the
old IP address.

PXYHOSTS :
66.59.184.37 www.york.ca

Actualy address from PING
www.york.ca : 207.35.67.132

I already try unload Proxy and then delete file "PXYHOSTS" and its
".sav" and then re-boot server. I display DNS cache entry for this site
(www.york.ca) after re-boot, it don't show any information. It show
back the old ip address after i use my browser to open this site
(actually it show gateway timeout on my browser).

What can i do? If its ISP problem why I can ping and reslove to the new
IP?

Isaac