Q: turned off iMessage and stopped receiving most texts

I ran out of data so turned off iMessage until the new month began but a week later established that most text messages had not been coming through to me (but a handful did and I had a normal text conversation with those few people).

Phone wasn't saying my texts hadn't sent and I have been told they were getting through, hence people replying, but most weren't getting through to my phone...

I had MMS turned on but not SMS - was that the problem? But why does that need to be on to receive...?

Thanks.