Mobile number should only accept Integers!

[imlegend19]

In models.py,

class Feedback(CreateUpdateModel):
     ...
     mobile = models.CharField(_('Mobile Number'), max_length=15, blank=True)

Since, mobile field is CharField, it also accepts characters which it should not!
To validate, you can employ some combination of formatting and then attempting to contact the number immediately to verify. You should use RegexValidator.