I'm guessing some info is missing from the story. I'd almost bet on some violation of the Fair Debt Collection Act on the part of BoA.
Or at least alleged, which was taken as truth because without BoA appearing to defend itself the judge cold only go on the couple's evidence\testimony.
In any case, it's not that they aren't a valid target for phone calls and such asking for payment, it's that there are indeed legal limitations in the law as to the extent. If BoA ignored them, they could submit a phone lot listing all the collection calls after they asked for them to stop, or started some process where the calls were supposed to stop, and at something like $2k* per, 500 calls later you're at $1M in legally mandated liability.
*State penalties for violating the DNC list range from $500 to $25k. I'm using it as a yardstick for the penalty per illegal call against BoA.