Generally you will be sat together unless

1. You pay to preselect the seats you want, or
2. Other customers have preselected seats such that there is not a group of 3 together remaining.

Unless you have leverage with the airline which seems unlikely given the conversation

You have the option to influence the outcome via 1. Otherwise you need to leave it in the lap of the gods and see if they sprinkle good fortune on you for 2.

The customer service staff you speak to have no means to allocate seats or tell the computer you want to sit together unless you pay for preassigned seats. And as per the comment above, yelling any anyone is not going to get you anywhere. The way the Qatar (and other airlines in the region) is run staff have certain responsibilities to do stuff and management do not generally look favourably on employees showing initiative or going the extra mile to bend the rules, so if they say they can't do it then you try a round of HUACA but otherwise you need to accept it.