Issues with keeping old number

I initially switched my old number over using a PAC and was fine. About a week later, I started noticing issues with my phone still saying I had two numbers, and people being unable to contact me on the number I wanted to keep (both phone and text) and receiving texts from me on the number I was trying to get rid of. My phone kind of flip flopped between using both numbers randomly. I went onto Live Chat to try and get it sorted, and she got me to reset the network settings on my mobile. I didn’t have another handset to check if this worked, so had to wait until I’d been chatting with my partner over text, and it seems that the number I wanted to keep has disappeared, and the one ID originally gave me is what I’m stuck with. I want to fix it, and get the number I wanted back, but every time I’ve tried to go on Live Chat since they’ve said that there aren’t any agents available. Any help at all would be very much appreciated