After years of no contact, do I still have to pay child support after a child turned 18?

In these circumstances, it’s unlikely that a court would order you to pay child support after a 2-year break in your now-adult child’s education.   There are several legal principles here.  First of all, it’s not a firm rule that your adult child must complete his or her academic program in the shortest time possible, in order to be eligible for support.  A brief pause in what is otherwise a linear education path will not disqualify him or her.  However, for situations where there has been a longer pause, the Ontario courts have developed a set of questions to determine whether an adult child’s entitlement to support can be revived after a break.  See the decision in Aubert v. Cipriani, 2015 ONSC 6103 (CanLII) at para. 28  where some of the guiding factors are set out.