Also So Cal here. Does your neighborhood offer multiple options for ISPs? I'd imagine this may be the case since they're offering a new customer promo. You should consider switching to the other ISP and then switching back to see if you qualify for the bonus.

We ran into this same situation and tried negotiating with Spectrum but ended up switching to AT&T (at the time they were conveniently offering $70/mo. for a 1 Gig line). When we informed Spectrum that we were not renewing services with them, the rep told us to keep our internet modem because they were so sure we'd switch back.

We hand delivered the modem to one of their offices and have been laughing now for nearly 18 months at their new customer promos that arrive in the mail.