The landlord may have a good relationship with the contractor aand trust his opinion.
The landlord may or maynot understand that the tech is a basketcase. Its not uncommon for landlords to pay people to do things they themselves know nothing about.
I would recommend hiring a tech on your dime and explain to him what's up.
Then before you make the repairs give the landlord a written copy of the problem and the fix. If he proceeds to give nil then have it fixed and contact your local magistrate and get the proper paperwork filed. Take him to court and recoup your money and your deposit.
But chances are.... he doesn't know how bad his "guy" is and will help get you cool. Trust me no landlord wantss to lose a tennant.