I phone not receiving group chat texts but someone is replying with my phone number

So my work uses group chats and recently about the last month I haven’t been getting the group chats even tho they have me added. Last night they got a text from me in the group chat but I never sent this message there’s no records on my phone I don’t recall sending a text and the group chat isn’t even in my messages, when they try to text the number or call it it goes to me but I did not send this text if they try to make a new group I don’t get it either. Someone is basically using my phone number and screening texts to them and replying without me seeing. What can I do!? New number time?