The reason you might want to bother is because it is possible that if VM's systems consider that you haven't returned it, those systems may charge £0 to your account, and then when they don't see a matching £0 payment proceed through to a credit reference agency flag for late payment or default, even though there's nothing actually owed. Common sense won't apply, (a) because this will be entirely automatic and involve no human input, and (b) even if you phone up, VM's agents will say anything to get you off the phone but often can't achieve workarounds on the clunky and sometimes dysfunctional systems.
This may seem dramatic, but we have previously seen reports from ex-customers saying they've had zero balances flagged as late or defaulted, and the consequences of a soiled credit history can be serious and usually only become apparent when something you want (eg mortgage, new tenancy, loan, new mobile phone agreement) gets delayed or even refused due to a flag on your credit history. And as such flags are visible to all lenders, service providers and even employers and prospective landlords for six years, it's not a risk worth taking.
