ABC tank cleaning cleaned sludge from my parents oil burner for there home Brooklyn New York

they cleaned the sludge out of the oil burner.  when they left the oil burner did not work right.  We called Petro oil comapny and they came every day for 5 days.  Petro told us that we didn't have enough oil in the tank for the pump to work.  we needed to get an emergency delivery of oil.  The paperwork said they put 120 gallons of oil back in the tank.  we only had 68 gallons.  we had not heat and hot water for 5 days.  I don't know if the work that they did caused the pump to break.  But once we know they did not put the oil back into the tank we stopped the check.  My parents are 75 years old.  how are they supposed to know if they did the work properly.  When we showed the paperwork to Petro they told us they didn't put the oil back into the tank.  it makes you wonder if they really put in what they say they do.  Then the person from ABC called my parents and was swearing and theeatneing them.  That is just not right.  my father said you pay for my emergency oil and I will pay what is owed.  They guy was screaming that we wanted service for nothing.  No we didn't we wanted the service done right and it you put 120 gallons of oil back in the tank that is what we expected to be there.  This issue in not sitting well with me as my parents are 75 years old how do I know this company will do anything to retailiate.