Being charged for something I did not ask for

Hello, I’m wondering if anyone can help? 

My partner and I had took out a package with Virgin last August for Broadband and basic TV. At the time of the order the seller on the phone was urging my partner that we take an O2 SIM card as part of the package as it was “FREE”. My partner explicitly told the seller “NO” as we both have sim contracts already and that we did not need it. Unsurprisingly the SIM card was sent out to us anyway regardless of us already saying no to it. To this day the SIM has not been used, yet we have just recently received a bill for the SIM card. After speaking to both Virgin Media & O2 about this they both keep passing the blame on to one another, which is making us feel lost on where to turn to next. Upon further investigation it turns out that an account has been set up for this SIM card without our permission or authorisation which seems a big strange to me personally. 

Does anyone know what we can do as we do not want to make payments for something we explicitly said no to and especially for something that was set up without authorisation from ourselves??

Thanks