Yes it will work telstra. here is a link to a site that explains the settings you need. https://apn-australia.gishan.net/settings/1046_6_telstra_apn_settings_for_lenovo_a1900.php
Are you able to use that sim in another device and it works? Does any error codes appear when you try to use it on the A1900?
Has the a1900 been unlocked to use on any carrier?