The allegations of hacking of personal webmail account with the help of unscrupulous system administrator clearly makes out an offence u/s 66 Information Technology Act r/w Section 120-B IPC. However, if the police is not registering the case, you can file a complaint with the court u/s 200 Cr.P.C. r/w 156 (3) Cr.P.C. by making submissions that cognizable offence is made out and the investigation by the Cyber Crime Cell is necessiated into the complex cyber crime for the recovery of alleged digital evidences to establish the offence of hacking and the same evidence is not into your possession, which can be recovered by the police only after registeration of the FIR as per the provisions of Section 154 Cr.P.C.
Simulataneously, you can file also file a complaint with the Adjudicating officer under the Information Technology Act, 2000 (IT Secretary of each state has been designated as an Adj. Officer under the ITA) and claim compensation, damages from the erring party. The alleged act falls within the provision of Section 43 IT Act.