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Please try the steps in our Network Troubleshooting thread.
If you're still experiencing the issue after completing these steps, post the template with your answers here and I'll have a member of the team get back to you as soon as possible.
I am having the exact same issue and it is not phone related as it is happing on both mine and my wifes phone. This is been happening for the last 2 weeks and as a result we have ran up a huge landline bill.
1) After pasing the end of the street the issue seems to be resloved.
2) Full post code is NG8 5FY
3) Occurs on both mine and my wifes phone - we have have reseted the handsets, however this issue only occurs at home within the postcode above.
6) The issue started 2 weeks ago and has not been resloved
7) Happens on all calls after 10 seconds or so. There is full reception before and after the call
Can you try your Sim Card in another phone as a process of elimination to rule out the phone or sim card that may be at fault. Try another Sim in your phone.
If necessary any Vodafone Shop can replace the Sim Card via a Sim Swap.