I moved in with my ex in Sept 2013 she left the property after 3 months, and I paid all the bills and rent until the earliest time I could get out of the contract, which was 8 months (may 2014) but she never took her name off the contact, am I entitled to claim half of the last 5 months rent back.

If her name was on the lease, yes. You would have to sue her for it.. then if you win collecting it might be the hard part.

I assume "ex" means ex-"significant other", not ex-spouse.

If the parties were married, this should have been addressed in the divorce decree.