Dr.Monzer Kahf, a prominent economist and counsellor states: Working with fake certificates makes your salary during all this period against your work and it is hard working too, but you were given this job based on fake certificates. If it were not for these fake certificates you would have not be given this job, certificates do matter for work, some of such jobs would require certificates for safely and for many other reasons that are very legitimate, my suggestion is: 1) try to change job as soon as you can to get out of this fake situation, it is Haram to continue in this lie-based situation 2) Make sincere repentance between you and God and try to give as much as you can in charity and make du’aa’ and Istighfar and other good deeds, 3) money you got as salaries and other benefits are for the work you gave and it is Halal InShaAllah although one may say that you would have given much less if it was without these lies, but these lies can only be responded to by what is given in Number 2 above, and 4) don’t tell any person about these fake certificates, destroy them and do not ever think of using them again.