Why won't my Samsung S6 work on Total Wireless as well as it did on Verizon?

We recently switched carriers (from Verizon to Total Wireless). My husband's $35 phone works great. My Samsung S6 that I bought a new SIM card for keeps having trouble connecting to the mobile network. The phone not make calls and give a roaming error randomly. Texts will fail to go through quite often. I spend over 8 hours with customer service with Total Wireless. They sometimes transfer me to Straight Talk and even Verizon. My husband went back to the Verizon store and they said the issue was due to the hierarchy of call/text importance. (Verizon post pay, Verizon prepay, Straight Talk, and then Total Wireless). Yet when my phone is not working my husband's phone works fabulously. He gets reception any place and any time. Any thoughts?

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