Advice Needed - Apartment Has No Heat

Hello everyone! I am seeking some advice as to if I have any grounds legally to get my apartment to fix our heat. My (24 f) and my husband's (27 m) apartment (in PA) temperature has been in the 60s all week. We put in a maintenance request and when they did not show for two days, we started calling the leasing office. We are on day 3 of calling the leasing office now and the past two days they said they had contractors on site to install a new heater and we should have better heat at the end of the day. I bought this the first time they said it, but the second time, I call BS. The first day they said a new heater was being installed a maintenance person finally showed at our apartment. He checked and said our heat was on, reiterated them installing a new heater, and promised to come back the next day to ensure we were warmer. The next day, he never showed. This is the same day the leasing office told us they were installing a new heater AGAIN. We have been FREEZING inside our own home for days. For reference, we always pay our rent on time, we have never had a complaint against us, and we have been in our home for about a year and a half. I'm grateful we do not have any kids living in our home in the cold, just us and the dog, but I feel our apartment needs to be able to provide us with basic necessities and we have been more than gracious. I fear I may have to threaten legal action or withholding rent payment soon, but want to ensure I can actually, legally, do anything first. Any advice appreciated. I wish I did not have to pursue this but it is important. TIA.