I had to return something to Lidl recently that was faulty.
They offered the current selling price as I had no receipt (my item had been reduced in the meantime).
I returned with bank statements showing the laser transaction, a printout from the national consumer agency, showing that bank statements can be sufficient and argued the case again.
They weren't budging, until I noticed the same item on sale at the original price. They then claimed that the displayed price on the day (original price) was a mistake, and then tried to argue that a 28 day limit applied to the return of faulty goods.
Eventually after making enough noise I got a full refund as a gesture of 'goodwill'.