Dear _____________
On __________ (date) I received your letter which indicated that I had a balance of ______________ (amount).
On __________ (date) I mailed a check to you in the amount of __________ (amount)
You should have received my check prior to writing your letter and I am, therefore, somewhat concerned.
If you have not received my check by the time this letter arrives, I would appreciate hearing from you as soon as possible so that I stop the payments immediately.
I will hold this matter in abeyance until I hear from you.