Disappointed in service

On 25 May I took my Nissan NP200 in for its service at Nissan East Rand. I was contacted and told that there is a part to be replaced that they don't have stock for. The stock would only arrive in 2 weeks and that they cannot assist me with a car for the period that my car is at their workshop. I also cannot get my car while they wait for the part as it is to risky too drive without it, can cause extra damage. Yesterday, almost three weeks later I had to phone and find out what was happening as I haven't received any feedback to date. I was told that the part would arrive by yesterday or tomorrow. A few minutes ago I was contacted and told that the part had not arrived in the country and that it would only arrive by next week 17 June. I understand that the part is not available in the country, but I am upset by the way I am treated, there is no effort to assist me while we are waiting, I'm just told sorry for the inconvenience, but we don't have any vehicles available while you wait, what must I do in the meantime? What guarantee do I have that the part will be here next week? (4weeks later?) Needless to say, I don't think I'll be buying a Nissan again.