Builders warehouse Disappointing service in the plumbing section

We orderd an Ariston 15 L Geyser Thermostat and paid for two months ago for our apartments which havetenants in them and were told it was being ordered and it was paid for, and to this day when we go to inquire about it in the plumbing department nobody seems to know when we will receive them and in the meantime our tenants our moving out because of lack of warm water and that is affecting our income, such appalling service from such a big and trusted Hardware store is disappointing, and to add insult to injury we have to go to the store for feed back