Maintenance charge not paid by tenant of unsold apartment

Hi,

Greetings. I am residing (owner) in an apartment where 6 out of 7 units sold. Even after 2.5 years of possession, the 7th unit was unsold and builder let a tenant for rental. The building maintenance is taken care by the association of owners. But the tenant is not ready to pay maintenance/common EB charges. Builder has left to Dubai in September 2017. How can we handle this issue?  Thank you.