We're with BT too. I've felt for years that our landline quality is rubbish. As I have some hearing loss I always use my mobile these days, and I try to get people ringing me up to use my mobile number, not the landline. I think it's all a bit of a scandal. My landline connection alone, before the cost of calls and internet are taken into account, costs more than my mobile plan (SIM only on my ancient but beloved iPhone 6S), which has unlimited calls, texts and 20 Gb data.