There's two sides to this. Firstly, in your favour, you have a right for your data and communications not to be snooped on. If you were to use one of their phones, that would not entitle them to listen in on it.
However, they could stop you calling premium lines and abroad, as this incurs cost to them. For similar reasons, they may end up traffic shaping and blocking some sites with typically high bandwidth profiles. Similarly, they may want to restrict content to keep usage down , as it is a shared service that could be impaired by allowing everyone to access high-demand high-use type websites, such as facebook. Incurring costs isn't really something that'd (directly) effect providing internet access, only how well the service is provided to many individuals.
I thin with many countries declaring access to the internet to be an intrinsic human right (or at least something close to that), this does make me wonder what kind of access that means. All humans have a right to use facebook? Maybe... I think the intention is more that all humans have the right to use wikipedia, or email, or many of the wonderful enabling technologies and services available through it, and arguably social networks can have a positive effects too. However, that right is mostly served by internet being available 'freely' at libraries and schools... places where it may be time limited and content restricted. Arguably they are not providing the unfettered access you may have a right to- are they obliged to do so?
Ultimately, using such things during class is counter to education and I certainly think they have a right to manage your behaviour and keep you focused on studying during classes and study breaks. However, in your recreational time, I'd argue they have no such rights. However, you have no such rights to demand they provided facebook at all if they had no internet, so there's a false sense of entitlement when you're provided with some restricted internet (or people circumvent those restrictions).
Ultimately, if you need facebook, get a phone with a data connection (that can act as a hotspot, if you want to hookup your laptop), and only use it outside of class. Hell, if you're feeling enterprising, offer up your phone hotspot to other people for a nominal charge (20p/cents) and you may end up covering a fair chunk of your phone bill too. As long as you're using it responsibly and outside of class, I'd fight tooth and nail for your right to do so.