払う and 支払う: payment and other uses of 払う
Distinguish shared payment uses from nonfinancial uses of 払う.
Paying money
払う (はらう) means paying in 「料金を払いました」. 支払う (しはらう) also means paying an amount and can be used in the same context. Neither verb alone specifies payment in cash.
「私が払います」 means 'I will pay.' 私 identifies the payer, not the recipient.
Explaining payment procedures
「代金は来月支払います」 says that payment will be made next month. 支払う fits billing or settlement instructions but is not wrong in everyday speech. Preserve the timing rather than translating it as already paid.
「支払いは済みました」 means that payment is complete. 支払い is the noun corresponding to 支払う and can appear on bills or notices.
払う with dust and attention
「服のほこりを払いました」 means brushing dust off clothes, and 「注意を払う」 means paying attention. 支払う cannot replace 払う in these nonfinancial uses. Their shared payment meaning does not make their full ranges identical.
「払う前に金額を確認します」 says that the amount will be checked before payment. Do not reverse the sequence or present both actions as completed.
Does 「まだ支払っていません」 mean there is no charge?
Show the answer and why
No. It means payment has not been made yet. Whether a charge exists or has been waived is separate.