Calls cut off after 29 minutes

[Lowey72]

After  having had full fibre BB digital voice installed in September, I am STILL going round and round in circles with Vodafone regarding my landline cutting off at 29 minutes and 40 seconds - but this is only on one number that I call. Have tested calling a couple of others and both were ok, calls in are also ok. However whenever I call my mum on her landline, which I do daily, it cuts off every single time. 
Allegedly the issue is with tier 3 support but to say they are the highest level of support they don’t seem to have a clue what they are doing. 
Have been passed about, different people ring me, they didn’t trace the calls they asked me to make so had to do them again, made a complaint but that didn’t resolve anything. The latest is “we can’t guarantee that the problem will be resolved” and “the team are working on it” which they’ve been doing for 2 months now. 
it is absolutely infuriating. Does anyone have any idea what could be causing this please? I have already suggested it’s a SIP issue, but they say they don’t think so because it’s only happening on one number that I call……

help appreciated! 

[Lowey72]

I forgot to add, the issue isn’t with my mums phone as this doesn’t happen to her with anyone else, and if she calls me we don’t get cut off. 

[Janey]

Hi @Lowey72 Thanks for your post and for taking the time to explain the situation. I'm sorry to see this has been going on for so long without a resolution, in your shoes I'd feel frustrated too! Given it has been so long, I'd recommend giving our Social Media team a shout. Whilst they won't be able to investigate this from a technical perspective, they can log the complaint and escalate it into the relevant teams for investigation. Let the team know you've posted here to and provide a link too, just so you don't have to explain yourself again.