DUDU-Meng it’s likely that the stored numbers start with +44 on the mobile phone instead of 0.
Assuming this is UK, as 07 is the start of a mobile device number
Both these examples will dial the same number.
+44 7123456789
0 7123456789
Not sure if you can accommodate this within the app? As to a normal user, it would not be clear that this is causing the issue.