Regarding Regularization of Contractual Employee

Iam working as Contractual Engineer in a CPSE PSU,from more than 05 Year without any single day gap of my service to PSU.My selection along with other staff was done on individual contract basis initially for 02 Years.which extended for another 02 years time to time without any gap,and I have completed almost 06 year.Some of other staff have completed about 15Yrs.of Contractual Service.I was recruited directly by PSU by qualifying in Interview followed by Medical Exam.In my Offer letter it was mention that I can't claim for regular service as this is project specific job and service will be terminated when project will be completed.But,apart from this Project Service,now my PSU is giving me additional charges for works other than Project.Its clearly mentioned in my offer letter that My engagement to PSU is for Project basis..And now I'm looking after individually various other works of this PSU along with Project Works.At a single time I'm having additional charges..also PSU have changed my designation for works other than Project. In this situation when PSU have already violated Contractual terms and conditions,may I claim for regular service?? As,I'm doing additional works other than Project for which I was selected,and I'm not getting any additional benefits also..They have changed my designation ..At a single time I'm working with two designation.Kindky reply and guide.