Lots of critical comments here, but this is OP's first experience of NHS maternity services, and it's okay not to have any idea what to expect!
I've found so far (22 weeks FTM) that the midwives/NHS maternity have been lovely people, but very overstretched and overworked and, frankly, crap with admin - especially on the everyday side. The best advice someone gave me was to lower my expectations. My booking appt was also very late, they lost my urine & bloods so I had to go back and do it all again, and basically dismissed when I was worrying about things, which made me (like you) concerned that I could trust them looking after me and my baby. These routine "niggles" I think have got quite a bit worse since the pandemic, as everyone has been overstretched.
BUT they are, generally, very good in an emergency. Mine never answer the phone to routine questions, but when I left a message with some questions one midwife called me back within a few minutes to say "hey, I got your message and was concerned, I think you need to go to A&E right now". (Luckily all was well, but it was definitely something that needed checking out.) Emergency services are still functioning throughout the pandemic, and you shouldn't feel bad about using them if you need them.
It is hard to trust that they'll be there for you in a crisis if they can't be there for you on the everyday questions/problems, but they will be. Your and your mum's experiences will have made you understandably wary, and please know that your worries are 100% natural. When you do get your booking call, do mention this to the midwife and she might be able to refer you to some perinatal mental health services - even knowing that someone will be on the end of the phone if you need them might reassure you!
Good luck and congratulations :)