We don't email receipts. Every charge - subscription renewals, prorated plan changes, wallet top-ups - is listed under Account & billing, each with its Stripe-hosted receipt link.
Upgrades take effect immediately and you pay only the difference for the rest of the period. Downgrades take effect at your next renewal, with no refund for the current period. Cancelling stops the renewal; your plan and credits stay usable until the period ends.