Pre Exisitng Disease in Health Insurance

My mother has a policy with leading medical insurance company which was started in Mar 2015 and continuing till date. Now from Apr. 2017, she is having health problem i.e Mennorhagia where Dr. has advised for and applied for Cashless but Star declined it. The reason for denial was that she had got Draining and cleaning done in 2009 which was forgotten and not disclosed while starting the medical policy and company is categorising current condition as Pre existing Disease and on non disclosure grounds they have declined the claim. I have gone through the definition of Pre Existing disease from Policy clause and it says the following: "Pre-Existing Disease means any condition, ailment or injury or related condition (s) for which the insured had signs or symptoms and/or were diagnosed and/or received medical advice /treatment within 48 months prior to the Insured's first policy with any Indian insurer" So my understanding is that Draining and cleaning done in 2009 doesnot qualify for being called as Pre Exisiting disease as it was beyond 48 months window please Help and advise