They create talk scripts that run to pages and create charts that correspond to the conversation.
If you say XX, they will reply with XX. Then you should reply with XX. They will always reply with XX... and so on.
Unfortunately, the receptionists who receive "don't know mobile number in cambodia anything" are professionals at receiving telemarketing calls. They can tell from the second word that you are speaking exactly as the talk script says, and they also fully understand whether the talk is beneficial to their company or not, and whether it is something they cannot judge for themselves. If the receptionist turns you down, it is proof that they find your telemarketing call very boring and not worth listening to, or that the timing was unfortunately not right and it was a very busy time, or that they do not need your product "right now."
I have been fortunate enough to have experience being both the one making a telemarketing call and the one receiving a telemarketing call, which has allowed me to acquire know-how that could be called the secret of telemarketing, and I would like to write about this know-how at some point.