SSH connection via remote proxy fails
I have an Unlimited Choice plan with 5 lines - 3 phones, 1 USB modem Netgear Momentum AirCard 313U, and 1 Netgear AT&T Mobile Hotspot Elevate 4G AirCard 754S. I used the USB modem with my laptop for remote access to a number of Raspberry Pis via the remot3.it service. Remot3 works similar to Teamviewer, and essentially provides a proxy (e.g. proxy8.yoics.net) and random port (e.g. 34256) for SSH traffic to bypass firewalls and NATs. It worked OK until recently, and now I get a message that network connection cannot be established or got reset by peer every time I try it. It just looks like the SSH protocol or ports provided by the remot3 service are blocked.
Does anyone have an idea if AT&T started blocking ports for Unlimited Choice accounts? What should I do to make the service work again? Would switching to Unlimited&More help or should I switch to some other plan?