Response to improper billing after payment

Dear On / / I received your letter which indicated that I had a balance owing in the amount of $ On / / I mailed a check to you in the amount of $ 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 inasmuch as I should issue a stop payment on the funds. I will hold this matter in abeyance until I hear from you.