Here is the sentence.
Where were you yesterday? – I was at home the whole day. – How strange. I (ring) you up at two o'clock, but nobody answered.
The Past Simple would be: I rang you up at two o'clock, but nobody
answered.The Past Continuous would be: I was ringing you up at two o'clock,
but nobody answered.
I am wondering why the authors of the grammar book where I took the sentence from tell me that I have to use the Past Simple. In my opinion the Past Continuous is more appropriate, for we have the exact moment of the action in the past.
Best Answer
As explained by englishpage.com, using the past continuous "was ringing" here would imply that the person had been ringing prior to 2 o'clock and was still doing so when 2 o'clock arrived. This is obviously not the case, which is why you use the past simple "rang". The relevant example with a similar usage:
"the Past Continuous is interrupted by a shorter action in the Simple Past. However, you can also use a specific time as an interruption."
Note that had the person ringing been interrupted, past continuous would have been appropriate. To wit: