Multiple Accounts, One Phone Number

I have multiple accounts with Xfinity.  But I only have one mobile phone.  Each account keeps pestering me to enter a mobile phone number to better secure my account; but Xfinity only allows one unique phone number per account.  So this security feature is worthless to me.  Is there any workaround to this problem?  Why doesn't Xfinity understand that their policy actually reduces, not increases, security?  And yes, I've complained several times.