Billed twice on my debit card

On 2 Nov 2019, negligent or maybe ********s cashier Innocentia at Hyde Park Corner billed me twice. At first she closed the till without me paying then she let me know of her ignorance and asked me to swipe my card, I agreed and paid for my goods but just when I left the store the bank notification came in my phone and bam there's 2 payment reserved for purchase at Pick 'n Pay Hyde Park Corner. I went back to the store and showed this cashier, luckily her manager Brenda was there and I showed her as well. She was not concerned at all...all she said is that it will reverse. But I asked her how it happened that I paid twice which she could not answer me. She told me that if it doesn't reverse I must return with a bank statement to the store. I went on Monday 5th and on Tuesday 6th I went with my bank statement (of which I want to know who's going to pay for that expense). I spent my entire lunch hour at the store with Brenda making numerous phone calls to try get this money back to me. Next thing she tells me to leave my details and she'll call me back as my lunch hour was over. I'm still waiting for that call with my money back in my account. I am really frustrated about this. I want to be compensated for the inconvenienced caused, the time lost fetching a bank statement, the cost of that bank statement and my lunch hour wasted at the store trying to resolve this and I want my money back. If this is some sick way of cashiers making money out of us during month end thinking we are ******** on our spendings then you have it wrong. I expect action in the next 48 hours because I'm itching to make Pick 'n Pay, Brenda and Innocentia very famous on Twitter.