This also happens in the States....here in Duval County, one hearing jail inmate, her mother was deaf. She asked to use the TTY in the jail to call her....the inmate was also calling long distances, and other local people that were NOT deaf! How she did it, I dunno....She has able to "dupe" the Relay.
Since hearing jail inmates cannot call out if there was a "block" on the phone, she was able to get around that....and also make long distance calls....FREE!....After about a week, the jail supervisor caught on to the "scam". Whether or not the jail inmate had to pay for those calls, I'm not sure.