Late promotion

Sir, I am working in a central public sector company (PSU). I was due for promotion w.e.f from 1st July 2014 under DPC -2014. Usually company would take interview in july and declare results by first week of August. However, DPC 2014 has been delayed by my management for long time and instead of taking interview for DPC-2014 in July2014 they took interview in Januray2015 and till date they have not declared the results. Further, my company has office order that revised pay/salary shall be given only after an employee joins the new post after promotion. This means that though I was eligible for promotion w.e.f from 1st July 2014, I would get new pay only after my results are out in 2015. Hence, by this policy of company, company has advantage in delaying the promotion/results as it will be saving money on employees salary because it need not to pay higher money till employees join the new post. As far as I know in most of the central government departments,employees get financial benefits wef date a employee is due for promotion and not from the date of joining new post. I would like to know , 1. Can a company delay DPC (Departmental promotion) like the results of DPC 2014 has not yet been declared. It seems company has no interest to take matter of employees promotion seriously. 2.Is the policy of giving new pay only after joining new post correct. It seems against natural justice wherein company is exploiting employee by denying fare financial compensation for delay in promotion. I feel company should give pay benefits with retrospective date since a employee is due for promotion irrespective of date of actual promotion/joining new post. Delay in DPC/promotion is company's fault.