Charged twice for one order

I placed an order last week on the 18th of April, after the delivery I decided to tip the driver. Instead of debiting my account with the extra amount for the tip of the driver they went and deducted the full amount plus the tip.

I raised this week and they gave a generic response to say I changed payment methods which was a lie, after telling them that I didnt do that. They went on to say the amount was a temporary hold. I then pulled bank statements to prove that its not a temporary hold. Then they said a refund has been processed. Today it has been about 2 weeks and the refund hasnt reflected. So I sent the query again only for them to go back and say I was never charged twice.

What puzzled me is how they give generic answers without doing proper investigations. I am pretty sure I am not the only customer that they have done this too, I wonder if this is their way of de*****ing us as customers.