Problems after switching from Verizon to Cricket

[VCBLS]

Bought S4 from Verizon five years ago. Bought sim and switched to Cricket 2 months ago. Suddenly, all my text messages fail to send and I cannot retrive voicemail. Also signal seems weak for this area. I have removed battery and sim, rebooted with the volume - on/off - home buttons. Cricket store tells me Verizon has locked something. Verizon says they don't do that. I suspect that this phone may contain some propitiatory Verizon firmware or software. At the time I went to Cricket, they assured me all was compatible and it would work fine - now, they want to sell me a new phone! Got any suggestions? Also, very weird, I can send texts and access voicemail when in Walmart or Cricket store!!??