You can very well pay the remaining salary and end up your notice period, but only it must written in your agreement or appointment letter. read your agreement or appointment letter carefully before moving ahead. you can file a complaint in your local govt. labour dept for your safer side.
1.1.3 Notwithstanding anything contained herein, during your probation period, Company may
terminate your employment upon thirty (30) calendar days notice to you or by paying your
monthly gross salary in lieu of giving such notice, with or without cause, and with or without
stating any reasons whatsoever.
1.1.4 If you desire to terminate your employment during the probation period, you shall provide
Company thirty (30) calendar days prior written notice with reasons for such termination.
There are few things that can be done in the situation you are in. You have to first check your contract with the company that weather it allows you to buy the notice period or the company had kept this option as per their discretion. If the contract says that you can leave by paying for your notice period than the company cannot bound you to complete your notice period and you can report to this issue to your locationâ€™s labour office about this and ask them to talk to the company on your behalf.
And if the company have kept this option weather you can leave or not is up to them than ask for the standing order of the company to check that the same is stated in it too.
Then we will take the actions as per the situation
18 Days shortfall is no earthshaking problem for an MNC.
Offer to pay shortfall and ask top management to be considerate and give you smooth exit.
What does your standing orders say about exit?
How long did you serve with the MNC?
Legal threat by company may not amount to much.
No court will take such a grim view if there is shortage of only 18 days and you have expressed your willing ness to pay shortfall to the company.
Going by the terms of employment you mentioned, it's clear that you don't have a Buyout option.
Did you inform 'in-writing' that you are joining the Govt sector & NOT another Company?
Despite all the various advantages in MNCs, the one disadvantage is about the Rules being more like in a Govt--rigid & without flexibility when left to the bottom-rung guys.
Like Nathrao suggested, the only option for you is to escalate to the Top--WITH a copy of the Govt Offer letter.
DON'T......repeat DON'T......harp on your side of the story about getting relieved earlier. Focus & sell the fact that the Company won't be effected in any way by your leaving now or later.....since you WON'T be joining another Company.
Focus on the usual human tendency/frailty about acting only when things effect oneself. Since your manager has given you the Clearance, you have a lesser headache.
The Worst-case-Scenario action would be what Venu suggested [he is right that Govt sector doesn't insist on earlier job Docs, UNLESS there's some criminality/legal issue involved].......joining even if you don't get the Docs here.
But I wouldn't suggest it as the direct step without trying your best to get the Docs.......for all you know, you may want to quit the Govt job later & join a Pvt sector Company. That's when your lack of connecting career Docs will effect your chances very badly.
MAYBE, you can use this fact in your discussions/mails to the Top guys [don't see any point to mention it to the junior HR guys....they wouldn't understand the sanctity you are attaching to getting out the proper way]......"that you CAN leave even without any Docs but DON'T WANT TO as you value your association with the Company".
It will only enhance your chances of getting relieved faster & properly.
All the Best.