Issue with Letter of Intent for apartment rental in Singapore

Hi Everyone, Need some help or advice for the situation below: We were looking for a whole unit since our current rental is about to expire hence we were contacting several agents to help us. Yesterday we saw 3 units and out of that, we are ok with the 2. In the first one even if the unit is out of our budget, the agent keeps on persuading us to try to negotiate and he will help if he can get approval of owner. Note that the owner is overseas so there is the landlord agent as another representative. Even if it is out of the budget, and after all the persuasions we gave in. Now because we had another appointment with another agent and we prefer the unit more, we wanted to secure it else the other group who placed their LOI will be able to get it for sure. Before we contact our second agent, we first called the first agent where we already sent the LOI and he did not picked up his phone nor responded to the message so then we go ahead and sent another LOI to the new unit. Our problem is after 2 hours that he was not contactable he sent a message telling us that the owner confirmed but he did not send any documents of proof of the confirmation. So I think in this case it is not fair for us to chase them on the proof because in the first place they should be sending the document to us as soon as possible. We gave them 12 more hours to give this and time has passed already and he is even not answering the phone. Can you tell us what to do? Regards, Jennah