Arrear maintanance

1. There are some crucial missing links !
2. In my opinion it is highly unlikely that due process of Court would not have been utilised by wife in last 4 years; they are "alternate mode of service" "paper publication" and then “ex parte” Order.
3. Nevertheless if you have received Notice today as you tell us then hire an seasoned advocate / LCI lawyer search and make first appearance with delay condonation and get same allowed and then file reply citing 4 years delay in receiving Notice which is no fault of yours.
4. Now diligently contest the maintenance case.
5. Regarding date of application Order; in S. 125 CrPC it is mostly awarded from date of application as it is a summery statutory provision and Magistrate has to give reasoning if awarding from date of Order. Even if you approach Sessions Court it is not clear from your query "if any maintenance awarded" or not but basics are replied under this para as to how to contest it now instead of roaster sitting on Notice that has been said to be received now! 
5. Never surrender before giving a tough contest in Family Law cases on points of Law with assistance form a seasoned Advocate otherwise your last innerwear will be auctioned off on negotiation table.