Basic items always out of stock after payment taken

I ordered online this morning and at the time, all my items were in stock. I then received an email stating items were cancelled due to no stock. These are basic items such as sanitary towels and sugar. This happens every time I order, at least 2-3 basic items which display stock online at the time of paying then are cancelled an hour or two later. Waiting period for refund is 2-10 days.