Slow wifi speeds / blackspots but can't order an additional wifi pod - help!

We've had VM broadband for a few months now. We had some initial speed issues and an engineer came out and replaced the router. We have a large 5 bedroomed house and he told us he would order an extra pod, but it never arrived. I managed to speak to a CS agent a while later and they also confirmed they would send an extra pod - never arrived.

Now when I try to do it via the app I end up going in circles where I can never actually speak to an agent to raise the issue despite logging slow donwload speeds / black spots in some areas of the house. Can someone please tell me how I can speak to someone to resolve this? Many thanks!