No Signal / No call / Why can I call " contact us" ?

I moved to Irvine (CA) last week. I'm new to the U.S.

I bought prepaid mobile USIM.

But it is so hard to call at home or around there. If you want to call, you have to go out to find a signal. Even I can't use the application over the phone because the signal is too weak at a mart or coffee shop near my house.

Please check this problem, otherwise we will need a refund.

In addition, Wi-Fi calls are not available on my phone, so it is not a solution. 

And I couldn't call the T-Mobile customer center, so I contacted the website. However, all T-Mobile information on the website says, "You have to call the customer support center." It's hard to borrow a cell phone because I just moved in. However, when I accessed your homepage, the information was also a phone number.

I sincerely hope there is a solution. I beg you.