3 have been charging me for 2 contracts and now say they don't have to refund me?

igetboredeasy

In December 2019 my Mobile contract with 3 was finishing.  I saw a new contract deal that was better than i could get on my upgrade so i signed up for it and requested to port my 3 number to 3.
I received a call regarding the porting and when i explained the reason the person said they could give me the same deal on an upgrade.  good so far. the plan paid off.
I went through the upgrade process with them and they said they had cancelled the other contract and to refuse the delivery of the phone.
I refused the delivery of the phone that was now cancelled.
All was good until i was checking my online banking in August and saw i had been paying for both contracts.
I contacted 3, they cancelled the contract and told me the phone that i had refused had been reissued to another customer. I was told they would issue a refund within a few days.  
This is where its gone a bit awry.
I contacted 3 several times to chase the refund and was told it would a be a few days each time..  after 4 chases i put out a disgruntled Tweet and someone contacted me and gave me a URL for a different support chat.

The person had a look and could see the tickets i had raised.
She then said that i was unlikely to get a refund as i had taken too long to contact them and there was no proof i had asked for the contract to be cancelled?
I told her that the timeframe is irrelevant, that the cancellation was all initiated by the 3 rep in december and was on the same call as my current contract upgrade and lastly that the phone i have been been paying for has been reissued to another customer so they have likely committed fraud.
The person said they would look into it but where not confident i had a case?  

So after all that what are my options?

Cheers in advance

Geoff