"You Are Roaming" Messages - Unable to make calls

I have a Samsung Galaxy SCH-i545 CDMA phone that I ported over to the straight talk network. Ever since I ported it over I am having an issue with roaming. When I am in certain locations, every time I'm there my phone will connect to a tower that will not allow me to make or receive any calls. When I try to make a call it plays me a message like "You are roaming. To purchase a pin number on the american roaming network press 1..."
I've called Straight Talk customer support on this issue several times, and each time they "reprogram" something on my phone and spend a half our to 45 min on the phone with them. The last time the operator had me go stand outside the building I was in and reboot my phone. It reconnected to the ST network. I asked him what he changed and he admitted that he didn't "reprogram" anything, he just had me reboot my phone. Every time I go into this building my phone gets on the "american roaming network" and when I leave the building, even though there is 4G verizon coverage outside the door, my phone will not leave the "american roaming network" until I reboot my phone or go in and out of airplane mode.
The weird thing is that when I search online, I don't seem to be finding others with this issue. Which makes me wonder if its particular to my phone, etc. I just don't understand why ST can't change the tower list in the phone to have it not connect to the "american roaming network". I would rather have no service on my phone that have it look like I have normal service and be unable to make a phone call.
I will add that sometimes when this happens it says "extended network" on the top of my phone and sometimes it all looks like normal.
This issue is really annoying and I'm thinking about switching from ST to another service if it cannot be resolved.
I've called Straight Talk customer support on this issue several times, and each time they "reprogram" something on my phone and spend a half our to 45 min on the phone with them. The last time the operator had me go stand outside the building I was in and reboot my phone. It reconnected to the ST network. I asked him what he changed and he admitted that he didn't "reprogram" anything, he just had me reboot my phone. Every time I go into this building my phone gets on the "american roaming network" and when I leave the building, even though there is 4G verizon coverage outside the door, my phone will not leave the "american roaming network" until I reboot my phone or go in and out of airplane mode.
The weird thing is that when I search online, I don't seem to be finding others with this issue. Which makes me wonder if its particular to my phone, etc. I just don't understand why ST can't change the tower list in the phone to have it not connect to the "american roaming network". I would rather have no service on my phone that have it look like I have normal service and be unable to make a phone call.
I will add that sometimes when this happens it says "extended network" on the top of my phone and sometimes it all looks like normal.
This issue is really annoying and I'm thinking about switching from ST to another service if it cannot be resolved.