Are you sure that Sri Lanka's Bank of Ceylon banned bitcoin? I'm looking for an article that has this news but the results are poor.
This is one of their latest statement: April 16,2018.
Public Awareness on Virtual Currencies in Sri LankaThey are giving warning to their people but there's no ban.
Many countries provide similar statements, not prohibit but warn the public to invest in bitcoin has a big risk, and this is the government's concern about the economic value of the community.