Text going to a number that has been deleted and doesn’t exist in my contacts

I deleted an old number from a contact, but when I tried to send them a text in a group message it used the old number, which isn’t in my phone anymore. When I send an individual text to them it uses the correct number. The old number isn’t listed in Gmail or iCloud and I can’t find the number anywhere in my contacts when I search the actual number. How is this old number jumping into the group text? I also removed the person from the group and made sure only the right number is in their info and then added them back in. It still reverted to the old number. Please help