Tata Sky — Unilaterally changing my balance amount and due date of recharge

Address:

142022

Dear Sir, My tatasky subscription number is [protected] . On 24/12/2015 I made recharge in my account of Rs 850/- . The new balance showed Rs 3351/- and due date of next recharge 12/05/2016. On 25/12/2015 I received message on my mobile number showing balance amount as Rs 593.80 and next date of recharge as 11/03/2016. Please explain me .