Hi! I was in a kind of similar situation as yours.
I was on a student visa finishing my Masters program at a good university. I had a limited number of days (60 days or something) to find a position. It is very difficult to get a job with a company that sponsors H1B visa. Fortunately, I was hired as a full-time intern at a company. The HR had said that after a probatory period of 9 months, I will be re-hired as a full-time employee. At the end of the internship, they just changed my status from intern to full-time employee, without any chance for salary renegotiation. I took it up multiple times with HR and my then manager, now department head. Following this, they increased my salary by $1/hr. It was like an insult. I also had my hands tied because they were sponsoring my H1B visa and if they fired me, I would have been deported. I will be completing my three years at this position in April. I was always disheartened when a new employee who I WAS TRAINING was making more than me (I prefer to have open discussions about my salary with my colleagues and they do the same). I brought this matter up with my new manager again. She said that she will talk with HR and suggested that it will be a stronger case if I had a job offer at hand. She also said that if changed the new salary will be in effect after the year-end performance review. I was being paid $67K then and wanted it to be $76K minimum. They changed it to $72K and said an 8% increase is amazing! When everyone got 2K year-end bonus, I got $500.
December 2021, I started looking for new positions. Finding and applying for H1B sponsoring companies is difficult! I was headhunted by a big pharma company. I had six interviews with them and they loved me and the work I do. I was all ready to negotiate my salary as I did not want to be lowballed again. I was expecting $85-95K this time. The offer they made completely blew me off my pants. So if everything goes good, I will be joining the new company early May! Fingers crossed! Wish me luck for a smooth visa transfer!
I will advise you to look for new opportunities! You should not be feeling being taken advantage of! It is the worst feeling ever! And you will not know your self worth unless you look for it! All the best!
Also to note, my current employers are really good people. Few of the best people I have come across in this country!