COMPLAINTS AGAINST A CONTRACTOR - PLS HELP

Good Day Everyone.
I have a problem with my contractor. Only recently I found out that they dont have a PCAB license.
Around October 2013, we hired them to do some finishing works of our Second Floor interior (plastering, tile works, paint, electrical). It was a Phase by phase contract and payment was made partially, and we still have around 30% balance due. But I decided to hold the payment because we found out that some materials were missing/uninstalled, and super overpriced. For example, they charged us 50pcs junction box, but on actual counting they only installed 23pcs..also in the contract they provided around 900pcs tiles but only around 400pcs were installed..and still more missing.
With regards to the price, for example: market price of Tile Grout is only P47.00/pack, 1pack Tile grout contains 2kilos..they charged us P1,250.00/kilo tile grout, and in other pages is P150.00/kilo.
I asked some licensed Engineers about their opinion on this and all of them told us that this contractor doesnt know how to make a decent quotation.
Now my problem is, I didnt know that they have to provide a so called blue print? Also, they dont have a PCAB license and their contract with us is Null and Void.
And they are forcing/harassing us to pay the balance and telling us that they dont want to finish the job anymore because they are upset because I did some market price research on all materials. they are upset because we questioned their contract.
Anyone pls help me assess my problem, some transactions are verbal but we have real evidence of the issue.
Now I want to know if we have the right to sue them and what would be the status of our case?
Pls anyone help..
Thank you so much.

Of course you can sue them - and perhaps winn the case after LONG time in court, depending of what evidience you have
BUT the question is - Is it worth it? Bad contractors have normaly much depts/ more people have demands on them, so I most likely they can't pay you if you winn (or no assets in THEIR name).

Do you live in a smaller town/village?
If so it can PERHAPS be worth going to the baranggay. They have kind of a "mini court" which can decide in SOME types of cases.

Then you have the BODY risk factor to thinl of to before you decide. Rather many have been even killed in the Philippines for SMALL things. A kill contract can cost as litle as 5000 pesos. For some it depend of "Lose face", for some it's just greed if it's cheaped to kill than to pay someone...

Try reading this. Hope you get something about entering into contracts. https://www.alburovillanueva.com/contracts