A letter/email of complaint regarding misrepresentation of products. It requests for a replacement/ refund/ special discount on the goods.
When we purchased the [Product] on [date] (order no. [number]), it was represented in the [promotional materials / product specifications] that it is [of certain specifications / fully compatible with certain products]. After trying it out, we were shocked to find that was not the case. The [Product] does not work [as it was advertised] / [for us as we require it to be compatible with our existing [system / product].