Firstly, sorry you experienced that OP. Hope you're feeling better.
I've got some experience of this as I work in HR. Things are not always as they appear. Some examples....
We had a house-keeping department that was manned (wo-manned!) entirely by women from one Eastern European Country, about 12-15 staff on average. We had a perpetual ad in the job centre for staff and would get British people applying (British people of all skin colours). The British people would start and would very quickly leave. The head of the Department, who was often the only British person, said this was due to British people not wanting to do menial work for minimum wage. Her deputy was the woman with the best grasp of English and was used as a translator. I always had her involved for the compulsory health and safety inductions and, as many in this department didn't speak any English, I assumed she told them which boxes to tick on the questionnaire. One British woman who left told me a different story though. She said that even those who could speak English refused to engage with her and I can certainly confirm that she sat alone in the canteen at break and lunchtime, effectively she was frozen out. Exclusion is a form of bullying and I'm not certain that the head of department's idea that British people are too lazy to do this work (which is actually rascist) is the reason so many left.
Likewise our kitchen porters. All "the children" (her words) of the Head of Department, but this time all originating from the same part of Africa. In my tenure we had one British person (recruited by the chef) taking the role and he didn't last the week.
So if people are speaking about immigrants monopolising jobs, then yes, the examples I give do reflect this. British people do apply for and take on menial roles for low pay, so the idea that they won't is another myth (as well as being rascist, as mentioned before).
Another myth is that immigrants come here for our NHS. I have worked with and become friends with people from all over the world. A couple of my Polish friends have invited me to stay with them if I ever need dental work because our services here are so expensive and shoddy. Another woman, from the House-keeping department I mentioned above, returned home to have her baby saying there was no way on earth that she'd give birth in a NHS hospital.
People cherry pick the arguments that serve their own point of view, but things are rarely black and white.