Samsung S20 FE not receiving texts from certain people

I’ve recently transferred to id Mobile and kept my old number. However, since the number has transferred across, I have struggled with text messaging. At first, my messages were going through to certain people using the original SIM number (were appearing blue in the chat, whereas other people’s outgoing texts were green and they were being received from the correct number). I’ve managed to sort that, but now those people who were receiving texts with the wrong number are receiving them correctly from me, but their reply texts aren’t getting through to me at all! I’m getting so frustrated with it! I’ve now been sent another replacement SIM from iDMobile which is programmed with the correct transferred number, but I’m still having the same issue! I’ll be cancelling my contract if this doesn’t get sorted! (Yes, I’ve checked my coverage, checked blocked numbers, switched it off and on again ...) Any ideas?