Thank you for that additional information, that will be helpfull in allowing me to advise you today.
As the flights were cancelled, and you paid Opodo, it is them not the airline you had a contract with and they who should be refunding you.
As they are giving you the run around you can issue them a formal letter before claim and should they not pay by the date your specify then commence a money claim against them air court.
I have attached a template letter you can use and a link to the online money claim.
You can also look at the credit card company, not with regards ***** ***** the payment, but rather a claim against the credit card company under s.75 consumer credit act 1974.
Under this act, where the party you have paid fails to complete the transaction or refund, the credit card company are held equally liable for the payment.
So, if the amount was more than £100, you can make a claim against the card company for the full cost of the flights purchased.
You need to contact the card company and inform them you wish to make a claim under s.75 consumer credit act 1974, and then will deal with this with you.