Canteen service

A contractor is providing canteen service inside our premises & charging GST @ 18%.

We are suggesting for 5% without claiming ITC on their inputs, because we are not getting ITC on canteen service & it is increasing our cost.

My query is that, can said contractor charge GST @ 5% on regular registration or he has to opt for composition scheme?

In composition scheme he can not charge GST from us, & it will be extra cost for him.