I'm 23, single; and studying in the UK. I have been in the UK for 5 years and, thank God, I didn't do any sins (drinking or Zina). I wanted to ask if sex dolls are Haram, because it is really difficult living here without a partner, and I don't want to get married until I finish my study and start working.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Allah Says (what means): {And they who guard their private parts. Except from their wives or those their right hands possess, for indeed, they will not be blamed - But whoever seeks beyond that, then those are the transgressors -} [Quran 23: 5-7]

Imam ash-Shanqeeti while commenting on the above verse in his book Adhwaa al-Bayaan, said: “Allah has stated that those who guard their chastity, i.e. from committing illegal sex as Zina and sodomy and so on, are the true successful believers. He also stated that guarding one's chastity does not prevent him from taking pleasures with his wife or what his right hand possesses (woman slave) and he is not to be blamed since this is his right according to the contract of marriage or ownership (of a slave-girl). But, whoever seeks pleasure in other channels and means; i.e. in other than his wife or slave-girl whom he possesses), then he is considered sinful and a transgressor who transgresses the Limits of Allah.
Therefore, we state that it is forbidden to use “sex dolls” for enjoyment and one has to guard his private parts except from his wife or what he possesses of woman slave.
Allah knows best.