Please understand that they under no circumstance can you be arrested for this. We do not have debtor's prisons anymore. Understand that creditors have been using increasingly reprehensible, immoral, and frightening tactics to force people into paying debts. If the payday company want their money, they must file a complaint in a Pennsylvania Magisterial District Court. Only after a full hearing on the matter can they obtain a judgment against you. Even then, you may have some defenses to paying the debt depending on the interest rate. I would suggest that you explain to the callers that you are aware that: (i) you cannot be arrested for failure to pay a debt; and (ii) the creditor must use the civil process to obtain and enforce a judgment.
I would also suggest getting in touch with personnel or the help line with the Pennsylvania Department of Banking. I started out my legal career working there and know that they investigate unscrupulous collection practices and usurious loans: www.banking.state.pa.us Visit their site and find the 1800 help line to call.
Disclaimer: This response does not create an attorney/client privilege nor does this response constitute legal advice.