unknown person in my property

I rented my spanish property to commence october through an agency (English) in Alhaurin Spain.
The person who signed the contract is not the one who is residing in the property. I recieved two months deposit and 1 months rent. My 1st payment of rent was due 26th november - I have recived nothing to date.
The agency assured me before I left for the UK that failure of payment by the tenant I quote "he would be given 5 days notice after the due date then he will be evicted".
I have since been in touch with the agency and they are saying there is nothing they can do although they have recieved 1400 euros to set the agreement up.
This unknown person is saying to the agent that he will call into the office to pay the rent, then he rings and says he's handing the keys back, then he is asking if he can pay next week. I am confused as to why the agent is dealing with this person who has nothing to do with the contract

My questions are: -
Can I ask this person to leave?
Can I go back to my property to live in it?
Will the police help me?
Can I turn the utilities off?
Can I authorise someone to change the locks?

I would dearly appreciate any bit of help/advice you can assist me with

Dear Madam,

The letting agency cannot enforce someone to be evicted from your property, that's not their job. I'm sure they notified your non-paying tenant as you instructed but that's all they can really do.

As per our article on Evicting Non-Paying Tenants I advise you to initiate an eviction procedure as soon as possible. You will have to appoint a lawyer to act on your behalf.

A new eviction law has been pre-approved which will greatly speed up the eviction process to the relief of everyone, except the non-paying tenant of course.

You can most certainly not move into your flat whilst the tenant is still there, regardless if they are paying or not, or else face the risk of being reported to the police. You cannot shut off the utilities nor change the locks. Please read our article which explains the steps you must take.

I take the opportunity to offer you our legal services: Tenant Eviction for a Spanish Property.