Dear :

I have just received your second bill for the [merchandise] I purchased from you on [date]. I assume that you had not yet received my check #(copy enclosed) for $ that I sent you on [date].

Please let me know whether the check has arrived. I would be happy to stop payment on the original check and send you another. We are very pleased to have you as our supplier and want to be sure that you receive our prompt payment.

Sincerely yours,

[name]

[title]