Advertised Item Out of Stock - Twice!

I bought a tablet on 3 Feb, order *** to be delivered on or before 16 Feb. On 12 Feb I received an email stating that the supplier was out of stock. I was curious how this could be as said item was still advertised on the website. After a call to the call centre I learned that the item was not out of stock as communicated. I placed the order again, order *** to be delivered 19 Feb - no delivery. On 20 Feb I received an email Ref *** stating that the supplier was out of stock and delivery will be delayed. It is unacceptable to pay for an item and wait 3 weeks for delivery, just to hear it is out of stock once again. Bad service!