Google Ads calls conversion are different from the ones imported on Looker Studio

Hi,
I created a Looker Studio dashboard to display Google Ads performances.
I used “phone calls” as a metric but it turns out the number of phone calls displayed on Looker Studio is 2-3 times higher than the number I have on Google Ads.
I created the same dashboard for around 40 different accounts and I have the same problem for all of them.
I did check the differences between lead categories and contact categories but it still doesn’t add up.
Did anyone already had this issue ?
Thanks a lot
Marion