Having difficulties updating a form

I am trying to create a form that will allow users to enter their address, country and other details. However I can’t seem to update said form

This is what i have written in models.py:

class User(AbstractUser):
    is_student = models.BooleanField(default=False)
    is_teacher = models.BooleanField(default=False)
...
class Mentor(models.Model):
    user = models.OneToOneField(User,on_delete=models.CASCADE,primary_key=True, related_name='mentor')
    linkedin = models.URLField(max_length=200,null=True,blank=True)
    COUNTRIES = (
        ('SA', 'South Africa'),
        ('NG', 'Nigeria'),
        ('KE', 'Kenya'),
        ('OT', 'Other')
    )
    address = models.CharField(max_length=500, null=True, blank=True)
    country = models.CharField(max_length=30, choices=COUNTRIES)
    invoice_name = models.CharField(max_length=200, null=False, blank=False)
    account_num = models.IntegerField(max_length=100, null=False, blank=False)
    bank_name = models.CharField(max_length=50, null=False)
    branch_code = models.IntegerField(max_length=25, blank=False)

forms.py

class TeacherSignUpForm(UserCreationForm):
    email = forms.EmailField(max_length=100)
    first_name = forms.CharField(max_length=100)
    last_name = forms.CharField(max_length=100)
    linkedin = forms.URLField(max_length=200)

    class Meta(UserCreationForm.Meta):
        model = User
        fields = ('email', 'username', 'first_name', 'last_name')

    def save(self, commit=True):
        self.instance.is_teacher = True
        user = super(UserCreationForm, self).save(commit=False)
        user.email = self.cleaned_data['email']
        user.first_name = self.cleaned_data['first_name']
        user.last_name = self.cleaned_data['last_name']
        user.save()
        mentor = Mentor.objects.get_or_create(
            user=user,
            linkedin=self.cleaned_data['linkedin'])
        return user
...

class MentorPaymentForm(forms.ModelForm):
    class Meta:
        model = Mentor
        fields = ('address', 'country', 'invoice_name', 'account_num', 'bank_name', 'branch_code')

views.py:

    def payment_view(request):
        user = request.user
        paymentform = MentorPaymentForm(request.POST, request.FILES, instance= user.mentor)
        if request.method == 'POST':
            if paymentform.is_valid():
                paymentform.save()
            return HttpResponseRedirect('%s' % (reverse('teachers:billing')))
        else:
            paymentform = MentorPaymentForm(instance= user.mentor)
        return render(request, 'classroom/teachers/app-student-dashboard.html', {'paymentform': paymentform})

and the html form:

<div class="form-group">
                        <label for="name" class="col-md-2 control-label">Name on Invoice</label>
                        <div class="col-md-6">
                          <div class="form-control-material">
                            <input type="text" class="form-control used" id="name" value="{{ paymentform.invoice_name }}">
                              {{ paymentform.invoice_name }}
                            <label for="invoice_name"></label>
                          </div>
                        </div>
                      </div>
                      <div class="form-group">
                        <label for="address" class="col-md-2 control-label">Address</label>
                        <div class="col-md-6">
                          <div class="form-control-material">
                            <textarea class="form-control used" id="address"> </textarea>
                              {{ paymentform.address }}
                            <label for="address">Address</label>
                          </div>
                        </div>
...
                      <div class="form-group">
                        <label for="country" class="col-md-2 control-label">Country</label>
                        <div class="col-md-6">
                            {{ paymentform.country }}
                          <select id="country" data-toggle="select2" class="width-100">
                            <option value="1" selected>South Africa</option>
                            <option value="2">Nigeria</option>
                            <option value="3">Kenya</option>
                            <option value="4">Other</option>
                          </select>
                        </div>

What is the error or unexpected behaviour that you are seeing? What do you mean by “can’t seem to update said form”?