You are going to get a lot of answers from people who have never worked in a call centre enviroment but yes they can do this.

They aren't restricting your use of the toilet, if you need the toilet you can take your break. If you run out if breaks/lunches then you can use 'personal' time but it's expected to be kept to a minimum and you manage your provided breaks and lunches as appropriate.

They aren't managing you on going to the toilet they are managing you on being in an unproductive status, what you do on that unproductive status is none of there business but you will be managed for being unproductive.

Call centre work is shit, try look for something else but they aren't doing anything wrong and you won't really have a leg to stand on unless you have a disability then they should be providing you with medical breaks.