Student Group Rent: One student is not paying the rent, what can be done?

[Who]

The company is correct

All of you signed a lease together as joint tenants
THAT means that all of you together are responsible for ensuring the rent is paid. But who pays what towards that rent is up to an contract between the tenants and nothing to do with the company.
As far as the company is concerned the only thing required is the total amount of rent is paid when its due.Its up to you all to ensure its paid, but if 1 dont contribute then the others must pay instead, otherwise the company can sue all of you or any one of you. (e.g the one who's got the most money).
If you HAD an agreement you would have to sue the non-payer for breach of the agreement. (but since you aint you have little chance in succeeding)

The company is also correct that you cant throw him out. HE is on the lease just as you are. so he has as much right to live there as you have,.even if he never pays a penny towards the rent.
(cos YOU never bothered to arrange a contract that says he MUST pay a penny)

(Even worse - If he is a joint tenant then he has a legal right to live there and come and go as he pleases
If you prevent him from coming and going then he can go find somewhere else to live, and sue YOU for the cost of him living there)

The reason it makes no sense to you is cos you never bothered finding out the legal implications of being a joint tenant before you signed the lease
There is NOTHING in a joint tenancy that requires any of the individual tenants to pay any specific amount towards the rent, Just that ALL the tenants together must ensure ALL the rent is paid.
To make sure all tenants pay their share of the rent (AND utilities) requires a separate contract between all the tenants and has NOTHING to do with the landlord or the lease

Its a shame cos you are in the same position as LOADS of other students (but they dont know it) who just signed a contract (the lease) and never gave a thought to the legal implications of what they were signing

If your parents have house insurance and added the legal pritection insurance they could ring the number you should have, otherwise go see CAB or a solicitor but it would appear there are no loopholes

Last thing
Its would be a waste of time contacting the college or uni
Your lease is a private contract between you and the landlord.and has NOTHING to do with them
They will not get involved nor say anything to the other party (cos if they did he could sue them)