Store update, insert, or delete statement affected an unexpected number of rows (0)..how do I resolve this issue

Question

Error:

Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded.

I am trying to upload a file into my database with few changes in it but each time it keeps giving me this error and won't update the values...

if (!addRecord) {
  if (currentShiipingAddress != null) {

    var shippingAddress = existingAccount.AccountAddresses.FirstOrDefault(m => m.Name == currentShiipingAddress.Name && m.AddressLine1 == currentShiipingAddress.AddressLine1 && m.AddTypeShipping == true);


    if (shippingAddress == null) {
      existingAccount.AccountAddresses.Add(currentShiipingAddress);
    }
    else {
      shippingAddress.PostCode = currentShiipingAddress.PostCode;
      shippingAddress.AddressLine1 = currentShiipingAddress.AddressLine1;
      shippingAddress.AddressLine2 = currentShiipingAddress.AddressLine2;
      shippingAddress.AddressLine3 = currentShiipingAddress.AddressLine3;
      shippingAddress.DateUpdated = DateTime.UtcNow;
      shippingAddress.AddTypeShipping = true;
      context.Entry(shippingAddress).State = EntityState.Modified;
    }

  }

  if (currentBillingAddress != null) {
    var billingAddress = existingAccount.AccountAddresses.FirstOrDefault(m => m.Name == currentBillingAddress.Name && m.AddressLine1 == currentBillingAddress.AddressLine1 && m.AddTypeBilling == true);

    if (billingAddress == null) {
      existingAccount.AccountAddresses.Add(currentBillingAddress);
    }
    else {
      billingAddress.PostCode = currentBillingAddress.PostCode;
      billingAddress.AddressLine1 = currentBillingAddress.AddressLine1;
      billingAddress.AddressLine2 = currentBillingAddress.AddressLine2;
      billingAddress.AddressLine3 = currentBillingAddress.AddressLine3;
      billingAddress.DateUpdated = DateTime.UtcNow;
      billingAddress.AddTypeBilling = true;
      context.Entry(billingAddress).State = EntityState.Modified;
    }

  }

  if (invoiceCurrentContact != null) {
    var existingContact = existingAccount.AccountContacts.FirstOrDefault(m => m.ContactEmail == invoiceEmail);
    if (existingContact == null) {
      existingAccount.AccountContacts.Add(invoiceCurrentContact);
    }
    else {
      existingContact.ContactEmail = invoiceCurrentContact.ContactEmail;
      existingContact.ContactName = invoiceCurrentContact.ContactName;
      existingContact.TenantContactPhone = invoiceCurrentContact.TenantContactPhone;
      existingContact.DateUpdated = DateTime.UtcNow;
      context.Entry(existingContact).State = EntityState.Modified;
    }
  }

  if (purchaseCurrentContact != null) {
    var existingContact = existingAccount.AccountContacts.FirstOrDefault(m => m.ContactEmail == purchaseEmail);
    if (existingContact == null) {
      existingAccount.AccountContacts.Add(purchaseCurrentContact);
    }
    else {
      existingContact.ContactEmail = purchaseCurrentContact.ContactEmail;
      existingContact.ContactName = purchaseCurrentContact.ContactName;
      existingContact.TenantContactPhone = purchaseCurrentContact.TenantContactPhone;
      existingContact.DateUpdated = DateTime.UtcNow;
      context.Entry(existingContact).State = EntityState.Modified;
    }
  }

}
else {
  if (invoiceCurrentContact != null) {
    existingAccount.AccountContacts.Add(invoiceCurrentContact);
  }

  if (purchaseCurrentContact != null) {
    existingAccount.AccountContacts.Add(purchaseCurrentContact);
  }

  if (currentShiipingAddress != null) {
    existingAccount.AccountAddresses.Add(currentShiipingAddress);
  }

  if (currentBillingAddress != null) {
    existingAccount.AccountAddresses.Add(currentBillingAddress);
  }

}

if (addRecord) {
  context.Account.Add(existingAccount);
}
else {
  context.Entry(existingAccount).State = EntityState.Modified;
}

This is where I am committing the changes to be saved but it turns out to give me the above-mentioned error

 }
context.SaveChanges();
}


}


}
catch (Exception ex)
{
  return "Import Failed : " + ex.Message + " " + counter.ToString();
}

return $"Supplier Account details imported successfully. Added { addedSuppliers }, Updated = { updatedSuppliers }";
}