Terrible online service

Bought a mobile phone online on the 26th of April. Advert stated in stock. Even up until today advert clearly states in stock. I ordered and paid for collection. Advert stated 21 days to complete order. I called on the 9th of May just to check as the only update I got from them was order in progress. Surley it should be quicker if you have the product in stock as claimed in your advert. I have ordered stuff from abroad and it reached me quicker. I was promised escalation and feedback on the 9th of May but received nothing. I called again today on the 17th of May but could not get a clear answer. Again i was promised feedback. Still waiting. How can it take this long if you have item in stock.