Noc

I am presently working in a Govt Aided school in Delhi.I was joined here in 2018 August.I am still on Probation. Now i have been selected for the same post in proper govt school and have been called for document verification.They will ask me for info about present employer and NOC from the same.I had not asked for any permission from present school as i had filled the form in 2017 when i was unemployed.How could I? I tried informing about the post i had applied for ,a few times but my applications were not accepted citing the reason of being on probation.They either deny taking applications or deny giving receivings for them absolutely.I have not even received my single pay slip even after giving application for the same.My NPS has not been deducted either. Now,i just want to get my NOC saying that i work here ,we have no problem in her joining and no lien will be left after resigning.But they are asking me to resign 1st,then receive it.I cant do that because i have no idea how long will it take before the joining.I would like to know what should i do in this scenario?I have got the offer of appointment only.There are still steps left in it like verification,medical,posting,etc.