As to the letter from Heathmill's solicitors, I will PM Vikas again, but I don't think my comments about the legal stature of the communication should be made public.
Secondly, as to filing suit. I am a lawyer engaged in a litigation practice, and as everyone knows, "to the man with a hammer, every problem looks like a nail." I tend to think that filing suit is the easiest and best thing to do, regardless of other issues people may have (e.g., a need for privacy in their economic dealings, which you lose when you go to court).
That said, I suggest that some companies engaged in debt collection and payday loan activities can be effectively neutralized by a concerted attack. Now a person could get into trouble trying to organize such a thing, but if the same company were hit with a hundred lawsuits all around the country at the same time, and have to hire a hundred attorneys all over the country to defend against those claims, that could get expensive. But that would be sort of like a cavalry charge, someone's going to get shot.
One thing that I thought of, though, is what if one were to get a judgment against, say, a payday loan company operating out of Belize (where you can't enforce your judgment against them)? If other people who owe that same loan company money were to submit to garnishment proceedings for the money they owe to the loan company, that could pay off both debts at once. I should explain 'garnishment'. If A owes money to B and B owes money to C, then C can go into court and ask the court for an order against A requiring A to pay C instead of B in satisfaction of A's debt to B. There does not have to be a bank account or employment situation involved, those are just the most common situations in which this stuff comes up. But if A owed money to Belize_Payday_Loans, which owes money to C, then if A were willing to be served with a garnishment summons (because A may not live in the state in which the judgment was obtained), then A could pay C and thereby extinguish his debt to Belize_Payday_Loans by means of an unassailable court order.