How should I do???

I just got a new position for 2 months, but a still part time position, only 2 days a week.

The fact is during the interview, they told me they can't hire person only work part time for them (I told them I was working part time for other company), but I told them I can leave the current company to work for them full time if get hird. Unfortunately I was still refused iby both email and oral due to my unfluent Englsih which is very important to negociate with suppliers.They told me they might choose one from one of the other 5 candidates.

2 weeks later the HR told me they would give me a 2nd,and then hired me.However, this time they changed the full time to a part time to me, said anyway you are working for another company part time, so doesn't matter to you. And ask me if I would leave for contiune to look for a new full time position? By the way they told me to test me if my English skill can be satisfied.

I have been working part time for 2 months and very hard, but still no one told me to change to full time, and I am so far the only one work part time there. 

ohhhh, really confused what is their plan, what are their concerns about my position,just use me temperaily till to find another person to replace me, or only keep me as a part time employee, without any benefits? What should I do to make things better? 

Much stressed during these 2 months,please, could you give any suggestions, what should I do??? Any suggestions will be very appreciated and helpful to me.