See if the purchase can be proved or alternatively payment can be proved for the purchase you can file a consumer complaint against cement merchant to recover the damages from him.

You need bills to prove that cement was purchased by you from the contractor 

in absence of bills you would not be able to prove your case of defective goods supplied by contractor

Cracks on wall may occur for many reasons for which inferior quality if cement may not alone be responsible.

Moreover after 7 years you can not prove that the cement was supplied by this particular man.

So it is better to forget this chapter due to lack of proper remedy after such a long time.

If you have made payments to him and can show the payment entry that will also suffice

1. You don't have the bills
2. Time frame is more than 7 years
3. Any businessmen can keep the bills maximum 3 years for his records.
4. Plus Cement and build construction there is long procedure of construction.
5. To construct a wall cement, sand, and rock is mixed and this mixture should be in well proportionate otherwise wall has crack on it.And there are further so many reasons, like proper water pouring, climate etc.
6. Who said cement was not good ?

Without Bill's how will you prove from where bags purchased. Issue legal notice, quite possibility, they may reply confirming the quality of cement , this way you will get proof. Than can file suit sitting report of engineer.

if you want to file a complaint before the consumer forum you should have a bill . 

You can file a case against him. He needs to pay for your damages

contractor is correct that warranty is of 5 years 

you have no evidence to prove contractor guilty 

You can file case against contractor's that he one who knows the cement and mixing the mixture for pillars or wall and use the cement accordingly.

I think RERA come after your completion of project so how RERA will be applicable?

RERA is applicable to supplies after RERA came into effect. Secondly, this rule dose not applies to supplier but builder who provides flat.

Dose not mean from whom he purchased, if he is selling his liability only. ANd same cement used for both pillars and wall.

Dear 

If you don't have the bills of cement how will you prove that cement was purchased from that particular merchant. 

So in this situation you cannot claim any compensation from the merchant.

If at all it was a sub standard quality you should have taken action immediately and not after seven years at your convenience.

No case may be maintainable at this belated stage hence you may not waste more on litigation.

In my opinion any legal action you may propose to initiate against this issue may not fetch you fruitful result, all your efforts will be in vain due to various factors involved in this.

Hence you may think twice about it and take wise decision at right time.

See since time has passed he can take defense for same but you can still file a claim explaining the delay why was it not reported previously. 

See he has sold it to you he is responsible see you can take chance and file complaint against the said person.