I grew up with home made jam from my Nan when she was still here, & then my mum. Mould on the top of a jar of jam that had already been open a while was fairly common back then. You’d just scoop it off & go about your day.

However this is shop bought jam, & as long as it was recently purchased, or even if it was sealed & within date but not recently purchased I’d still complain to the shop or manufacturer, as I’d expect better from commercially made produce.