Very bad customer service from Cell C regarding upgrades

I did an upgrade to an existing contract last week. At no point was I informed that there were any stock availability issues. I phoned in 2 days later to enquire about my delivery, only to be informed that there is no stock available and it will only arrive this week "some time". I phoned in again this morning, just to be told the same story. At no point was I ever contacted or informed about any stock shortage or delay in delivery. I just spoke to a supervisor/manager in the upgrades department, who is still not able to tell me when stock will be arriving. Surely a big company like Cell C will not tolerate any delivery dates from suppliers as "some time next week", why should we as the customers that pay for the service have to accept such an answer??? They are in effect advertising and signing up contracts on a product that is not even available yet!