Why do my dismissed notifications keep showing up?

I have a thing with ignoring and not opening all my WhatsApp chats. I ignore them and dismiss said message notifications from my notification bar.

However evertytime new messages come in, the notifications of these old messages always pop up again. Any advice on how to prevent old and dismissed notifications from showing up again?

Eg
Tom texts me on WhatsApp. I do not open the message, and clear the notification from my screen. When Janet texts me later, I get the notification for Janet, and at the same time, the notification for Tom reappears on my screen. The notification for Tom's message reappears evertytime I get a new text. Is there anyway to permanently ensure old notifications not reappear anymore?

Thanks in advance guys!!