An open letter to Lidl

Dear Lidl,
Every weekend throughout the UK you advertise a series of ‘special offers’ on a range of products in order to entice people to visit your stores.
I would be interested to know why every time I have visited your stores in the last year, when I purchase any of the 'special offer' items, on examining my till receipt I discover that I have been charged the normal FULL price.
This is happening to me on such a frequent basis that I can't help thinking this is a sneaky attempt to rip-off your customers.
You must realise that only a small proportion of customers will bother to check their till receipts. And you must also realise that when they discover they have been overcharged, most of them won’t bother to go back to the store to ask for a refund.
Earlier tonight I purchased a bottle of wine from one of your stores which was clearly marked as being on special offer. On checking the till receipt I realised I had been charged the normal full price (yet again).
But trying to get a refund is like trying to extract teeth.
Firstly, I had to go back into the store and wait for the till operator to become free (and there was only ONE till operator working in a busy store).
The till operator then had to hold up the entire queue so that he could go to check the price on the shelf. He then had to get the manager to come out of the store room to issue a refund. This took about 15 minutes because the manager (as usual) was on his lunch break, or more likely he couldn’t be bothered to come and give me my refund.
When this happens it’s extremely embarrassing to have to explain you have been overcharged (usually by only a few pence) in front of a long queue of annoyed shoppers who have been held up while the shop arrange to give you a refund.
Tonight I was overcharged by 44 pence on my bottle of wine.
I really couldn't care less about the money itself. But I always insist on getting a refund, on a point of principle.
This constant overcharging by Lidl NEVER happens to me at any of the other big supermarkets like Asda, Tesco, Sainsburys, or Morrisons. Why is it only at Lidl? I am very suspicious about whether something rather duplicitous is going on.
Your company must realise that people are unlikely to check their till receipts. And even if they do check their receipts, they usually will not want to go to all the inconvenience and embarrassment of asking for a refund.
But if you add up all the numerous other shoppers who are also being overcharged, this amounts to a very large sum of money that you are making out of these 'special offers’ that are charged at full price.
So my question to Lidl is this:
Am I just 'unlucky' that this happens to me every time I visit your stores? Or are you deliberately trying to rip-off customers by advertising 'special offers' but then charging customers the full price, hoping that they don’t notice?
I look forward to your reply and will be happy to publish it on this website.
Yours sincerely.