Can a company prevent me from joining client company

I am working with outsourcing company since last 15 years. in my appointment letter below conditions are mentioned - 1 ) You will devote the whole of your time, attention and skills to the Company during your employment and will use your best endeavors to promote the company & undertake not to do anything against the interest of the Company. You hereby agree not to hold or take any other office employment & occupation ( whether paid or unpaid) and whether or not competing with the business of company nor to hold shares other than in a company which is listed on recognised share exchange without companies prior written consent. 2) Ninety days notice will be required on both the sides for the termination of employment 3 You will be governed by the applicable rules and regulation of our office. 3) You shall treat all information / data of company & client of company, available to you during your employment as strictly confidential and shall not part with or share thedata with anyone during or after your employment with Company. My current company and client entered into the contract that they can not inhouse their employees. The gap between the resignation and joining should be 6 months or more. My client is offered me to join there organisation. If i serve 3 month notice which is mentioned in my appointment letter- -Can my current organisaction restrict me on joining ? & what if i am going to join to other departments with same client. -After I have put my resignation and served my notice period. Can the company restrict me from giving my relieving and experience letter? - Is there any impact to received gratuity & final settlement ?