I think "Upon completion of the Job" means little as some would say there is no fixed deadline - a job would still have been completed 3 months afterwards. Take a change of tack.
Payment is due "Upon the date of completion of the Job".
Also, "Where payment in full is not received within 7 days of the date of completion of the job a penalty rate of 2% per calendar month or part thereof will apply calculated from the date of completion of the job until full payment, including the penalty sum, is made. Legal action will be taken for recovery of the full amount, or such sum as may remain owing, 90 days after the date of completion of the job".