If it's the same number and people are still sending messages to the group then you should still receive them. So first thing would be to check whether messages are still being sent that include you.
If they are and you are not receiving them, then can you send/receive picture messages (MMS, not Snapchat etc)? This is relevant because many carriers/individuals send group messages as MMS, so it may be that it's MMS that's not working for you rather than this particular thread. If there is a problem there, check your APN settings - some carriers use separate APNs for data and MMS, so it's possible for data to work and MMS not to.
