Not sure where they are going about the suitability of the chair, but I do understand the need for proof of purchase.
If you had the receipt Im sure you would have been refunded / had the chair replaced instantly.
Try taking a bank statement to the shop....
In each of their replys they request some sort of proof of purchase, in none of your replys do you mention you have the receipt, or can prove it was bought there by bank statement.
Im not doubting you did purchase it from there, but in their eyes you could have picked it up from the tip and are trying to get cash out of them.
Help them out with their proof of purchase requests and they may become more helpful
