Call them and ask to speak to the VP of sales. Explain your situation, reiterate the amount of business you do with them monthly or yearly and invite them to check out your website.
I've had this same problem with a couple of vendors and once I've done the above, they've all come around.
Good Luck... it's frustrating, I know.
..Marisa
www.paperaddict.com - miva merchant store, est. 2001.
www.goldkeydecor.com - 3dcart store opening late April 2008.