Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE CUSTOMER (LastName VARCHAR)
TABLE: CREATE TABLE CUSTOMER (LastName VARCHAR, CustomerId VARCHAR)
TABLE: CREATE TABLE Invoice (CustomerId VARCHAR, total INTEGER)

### Question ###
Find all the customer last names that do not have invoice totals larger than 20.

### Accurate SQL ###

SELECT LastName FROM CUSTOMER EXCEPT SELECT T1.LastName FROM CUSTOMER AS T1 JOIN Invoice AS T2 ON T1.CustomerId = T2.CustomerId WHERE T2.total > 20