customer service honestly sucks

Having the worst experience with Birkston's online. I need to exchange my shoes for a smaller size, I logged my return on the 30 Aug 2022, 3 waybill numbers were sent to me with different days of collection and my shoes were only collected on the 15 Sep.

I emailed the head office to find out what is happening the staff member confirmed the item I needed exchanged and then sends me an invoice to pay an extra amount when it was the exact same shoe just in a different size. I then call in to find out why I need to pay extra for them to tell me it's an error on their end and not even apologising and then for the lady to tell me the shoes I'm returning never got to their warehouse yet and it still needs to go through the exchange examination process.

Explain how the hell can you can send me an invoice to pay in extra when the shoes I'm returning is not even at the warehouse??

This entire return process has been a mission and customer service honestly sucks