If this was a BA flight, the FA is wrong - I would have walked up to the Purser and calmly informed her of the conversation with the FA, the FA's attitude in not enforcing the safety rules and you would would write to to BA and CAA quoting the FA names and the Purser as the staff member being overall in charge.

This is not acceptable for BA. The moment that a plane takes off and land are the more critical in terms of safety. Poor show if BA does not take interest in this.

If the FA could walk over to you, I take it that this was some time after take off. She may have heard the bit about the seat hitting your knee but not the timing when the seat was reclined.