Dear _____________
On _______________ (date), I attached my letter to the merchandise I returned to you and requested a refund for same. I have enclosed a copy of that letter for your convenience.
As you will note, quite some time has elapsed since I initiated my first correspondence, and I have not yet received your check. I would appreciate it if you would tend to this matter as quickly as possible, since I am sure that you can understand my reluctance to order any additional merchandise from you under the present circumstances.
Thank you for your prompt attention to this matter.