Everything I have read about Verizon's throttling policies say what most of you have also said. They will only throttle you during peak times of tower saturation. Unlike AT&T, Verizon is not supposed to throttle users for the remaining balance of the month once started. I don't ever trust anything any CSR at Verizon says. They pretty much have zero information, or understanding of information.
I agree with trparky, is there a way for you to go to another town and see if you have data issues. If this is the case, I would say a)something is wrong with your device, or b)something has gone screwy with your account. A few years ago, something weird happened in my account that call forwarding started randomly happening, and was forwarding some of my calls to my g/f's phone. I had to have them permanently remove call forwarding from my account to correct the issue. No one could figure out why this was happening.
Good luck, I hope you get it straightened out.