"Operation cancellations"

Was in Grantham hospital one day in Oct at 7.30am for a right shoulder operation, went through all the admissions protocol and sat waiting then at 3.30pm was told the procedure has been cancelled due to staffing issues. So two weeks later i got a new date,  but in Lincoln hospital at 7.00am, went through the usual protocol and was assured that everything is running normal, so just sat waiting then at 5pm ( 10 hours ) was approached by duty nurse and was told the procedure has been cancelled. So my concern is that when i get another re arranged date how do i get some reassurance that the operation will go ahead !! So i need to be first in line to have the operation and not going through the same again.