Query

you can take back the complaint by stating that the concerned department assured to do to the work

but why tell the police to wait for some time as you are follwoing with the department and they assured you to complete the procees and if they do not do then you can intitiate action 

request them by oral words 

From your question it appears that police is yet to register FIR on the basis of your police complaint. If this is so, you can request the police for withdrawal of your police complaint, also requesting them not to take any further action on that complaint. Generally speaking, the police will oblidge you. However, the hard copy of your original police compliant may not be returned to you, since the police may have to retain it for their record, in view of the fact that they might already have given a regular complaint number. 

On the other hand, if the police has already registered FIR on the basis of your complaint, it can be withdrawn only in accordance with the provisions of S. 320 of Cr.P.C. relating to compounding of offences. 

@Querist,

1.No, you cannot hard copy of complaint back. It's for record purpose for the police.

2.Don't be over suspicious and without reason.

Note-This reply should be taken as per the declaration given in my profile page.

Thanks,

Regards,

You can make a written request for getting back the hard copy of the complaint, stating in your application the reasons why you want the hard copy. However, generally they may not return the hard copy, since it froms part of their official record.

But, in most cases where the FIR has not been registered, only a formal or no enquiry may be conducted by police and then be forgotten forever! The police finds it difficult to handle even the regular registered FIRs, most of the other complaints may simply be ignored by them. 

So, in most probability, if you do not pursue the case, the police might have already ignored it.