BJ's Warehouse Coupon taken on original purchase and then not honored on exchange. Bethlehem Pennsylvania

The company took a coupon from me for a Fitbit purchase.  Wehn I exchanged, it they would not honor it for the new item even though the item was included in the coupon and coupon had not expired.  The person at the store could not understand how to handle this, so I thought I would try doing it through this site.  After a few back and foths via email, they finally said that they undersstood but that I would have to handle it at the store.  

Then customer service experieince was bad in both cases, and I think that they used the coupon but did not give me the benefit of it.