diff --git a/core/models/billable.py b/core/models/billable.py
index 2f7009f..8c30e19 100644
--- a/core/models/billable.py
+++ b/core/models/billable.py
@@ -5,7 +5,6 @@ from core.models.profiles import ClientProfile
 from core.models.brands import Brand
 from core.fields.base import LongCharField
 from core.fields.numbers import CostField
-from core.models.invoices import InvoiceItem, Invoice
 
 from dateutil.relativedelta import relativedelta
 
@@ -38,6 +37,8 @@ class Billable(Model):
     recur_count = PositiveIntegerField(null=True)
 
     def next_invoicing(self):
+        from core.models.invoices import InvoiceItem, Invoice
+
         try:
             invoiceitems = InvoiceItem.objects.filter(billable=self)
 
diff --git a/core/models/invoices.py b/core/models/invoices.py
index 563dc9f..0fd46b7 100644
--- a/core/models/invoices.py
+++ b/core/models/invoices.py
@@ -2,13 +2,13 @@ from django.db.models import Model, ForeignKey, CASCADE, PositiveIntegerField, T
 
 from core.fields.base import LongCharField
 from core.fields.numbers import CostField
-from core.models.services import Service
 from core.models.profiles import ClientProfile
 from core.models.local import Currency
-from core.models.billable import Billable
+from core.models.brands import Brand
 
 class Invoice(Model):
-    client = ForeignKey(ClientProfile, on_delete=CASCADE)
+    client = ForeignKey(ClientProfile, on_delete=PROTECT)
+    brand = ForeignKey(Brand, on_delete=PROTECT)
     number = LongCharField()
     created = DateField()
     due = DateField()
@@ -16,6 +16,9 @@ class Invoice(Model):
     currency = ForeignKey(Currency, on_delete=PROTECT)
 
 class InvoiceItem(Model):
+    from core.models.services import Service
+    from core.models.billable import Billable
+
     invoice = ForeignKey(Invoice, on_delete=CASCADE)
     sort = PositiveIntegerField()
     name = LongCharField()
diff --git a/core/models/products.py b/core/models/products.py
index bab7de0..1515c1e 100644
--- a/core/models/products.py
+++ b/core/models/products.py
@@ -1,9 +1,8 @@
-from core.models.billable import CycleChoices
 from core.fields.base import LongCharField
 from core.fields.color import ColorField
 from core.fields.numbers import CostField
 
-from django.db.models import Model, IntegerChoices, PositiveIntegerField, ForeignKey, CASCADE, CharField, TextField, ManyToManyField
+from django.db.models import Model, PositiveIntegerField, ForeignKey, CASCADE, CharField, TextField, ManyToManyField
 
 from importlib import import_module
 
@@ -34,7 +33,9 @@ class Product(Model):
 class ProductPlan(Model):
     product = ForeignKey(Product, on_delete=CASCADE)
 
-class ProductPlanItem(Model):    
+class ProductPlanItem(Model):
+    from core.models.billable import CycleChoices
+
     plan = ForeignKey(ProductPlan, on_delete=CASCADE)
     cycle = PositiveIntegerField(choices=CycleChoices.choices)
     count = PositiveIntegerField()
diff --git a/core/models/services.py b/core/models/services.py
index 6f8378d..02b35ed 100644
--- a/core/models/services.py
+++ b/core/models/services.py
@@ -1,5 +1,3 @@
-from core.models.billable import CycleChoices
-from core.models.products import ProductGroup
 from core.fields.numbers import CostField
 
 from django.db.models import Model, TextField, CharField, ManyToManyField, ForeignKey, CASCADE, PositiveIntegerField, OneToOneField
@@ -10,6 +8,8 @@ from logging import getLogger
 logger = getLogger(__name__)
 
 class Service(Model):
+    from core.models.products import ProductGroup
+
     name = CharField(max_length=255)
     description = TextField(null=True, blank=True)
     handler_module = CharField(max_length=255, null=True, blank=True)
@@ -35,7 +35,9 @@ class ServicePlan(Model):
         for item in productplan.serviceplanitem_set:
             ServicePlanItem.objects.create(plan=plan, cycle=item.cycle, count=item.count, cost=item.cost)
 
-class ServicePlanItem(Model):    
+class ServicePlanItem(Model): 
+    from core.models.billable import CycleChoices
+   
     plan = ForeignKey(ServicePlan, on_delete=CASCADE)
     cycle = PositiveIntegerField(choices=CycleChoices.choices)
     count = PositiveIntegerField()