As mentioned just above, the verb "to doubt" + object is "douter de" + objet. The preposition "de" is necessary. And because "en" replaces "de" + object, you have "nous en doutons." Using "le" here is not correct.
Also, I would translate "we are in doubt" as "having doubts" in French, as in "nous avons des doutes", or even "we are not sure": "nous ne sommes pas sûrs".
I got a negative effect from doing this exercise: While keep being reminded "douter DE +qqs", I wrote the English as " we doubt ABOUT it". - and it was wrong. -- You may have recognized that I am NOT English mother-tonged.
So I need to remind myself that French "douter +DE", but english is "doubt" alone.
Firstly, you can know it's not "nous ont du temps" because the verb conjugation is wrong: it should be "nous avons du temps".
Secondly, "nous ont du temps" is not pronounced like "nous en doutons":
/nuz_õ dy tã/ vs /nuz_ã dutõ/ the vowels are different. I know that nasal sounds (especially 'an' and 'on') can be difficult to distinguish for learners, and the quality of the TTS doesn't help, but a native speaker will have no problem telling them apart.