diff --git a/database.py b/database.py
index ee51c8b..4bdbfe4 100644
--- a/database.py
+++ b/database.py
@@ -1,7 +1,7 @@
 import typing
 from sqlalchemy import create_engine, Column, ForeignKey, UniqueConstraint
 from sqlalchemy import Integer, BigInteger, String, Text, LargeBinary, DateTime, Boolean
-from sqlalchemy.orm import sessionmaker, relationship
+from sqlalchemy.orm import sessionmaker, relationship, backref
 from sqlalchemy.ext.declarative import declarative_base
 import configloader
 import telegram
@@ -69,6 +69,11 @@ class User(TableDeclarativeBase):
         else:
             return f"[{self.first_name}](tg://user?id={self.user_id})"
 
+    def recalculate_credit(self):
+        """Recalculate the credit for this user by calculating the sum of the values of all their transactions."""
+        valid_transactions: typing.List[Transaction] = [t for t in self.transactions if not t.refunded]
+        self.credit = sum(map(lambda t: t.value, valid_transactions))
+
     def __repr__(self):
         return f"<User {self} having {self.credit} credit>"
 
diff --git a/worker.py b/worker.py
index 2361a81..4de75af 100644
--- a/worker.py
+++ b/worker.py
@@ -505,8 +505,10 @@ class ChatWorker(threading.Thread):
                                      value=value,
                                      order_id=order.order_id)
         self.session.add(transaction)
-        # Subtract credit from the user
-        self.user.credit += value
+        # Commit all the changes
+        self.session.commit()
+        # Update the user's credit
+        self.user.recalculate_credit()
         # Commit all the changes
         self.session.commit()
         # Notify the user of the order result
@@ -663,10 +665,9 @@ class ChatWorker(threading.Thread):
             transaction.payment_name = successfulpayment.order_info.name
             transaction.payment_email = successfulpayment.order_info.email
             transaction.payment_phone = successfulpayment.order_info.phone_number
-        # Add the credit to the user account
-        self.user.credit += successfulpayment.total_amount - int(total_fee)
-        # Add and commit the transaction
-        self.session.add(transaction)
+        # Update the user's credit
+        self.user.recalculate_credit()
+        # Commit all the changes
         self.session.commit()
 
     def __bot_info(self):
@@ -957,8 +958,8 @@ class ChatWorker(threading.Thread):
                 order.refund_reason = reply
                 # Refund the credit, reverting the old transaction
                 order.transaction.refunded = True
-                # Restore the credit to the user
-                order.user.credit -= order.transaction.value
+                # Update the user's credit
+                order.user.recalculate_credit()
                 # Commit the changes
                 self.session.commit()
                 # Update the order message
@@ -1005,7 +1006,7 @@ class ChatWorker(threading.Thread):
                                      notes=reply)
         self.session.add(transaction)
         # Change the user credit
-        user.credit += int(price)
+        user.recalculate_credit()
         # Commit the changes
         self.session.commit()
         # Notify the user of the credit/debit