Why am I having signal problems/only one bar as soon as I switched from 3 to vodafone? Is waiting for my number transfer causing this?

I have been on the phone to customer service/technical team from vodafone who took me through a few troubleshooting steps which only brought me up from 1 to 2 bars. When it was only on 2 bars I couldnt even make or receive calls, this is why I rung them. They also said because I am using a pac code to transfer my ood number it tends to cause this issue? Is this true? When my number transfers will the signal issues be sorted? Also its causing my 4g not to work. Only my wifi and 3g are working atm and getting 2 bars.