Copyright: someone copied my content, software or images. What can I do?

First confirm you own the copyright and that no statutory exception applies. Then choose between a takedown request, a notice and a suit.

High complexity - significant legal consequences

Collect dated evidence: screenshots with URLs, copies, purchase records, and proof of your own creation date.
Copyright arises without registration, but a registration entry is prima facie evidence of the particulars recorded (section 48).
For online copies, ask the platform to remove them; many have copyright complaint procedures. Section 52(1)(c) also requires a service storing a copy for linking or access to stop facilitating access for 21 days on a written complaint.
Civil remedies include an injunction, damages and accounts of profits (section 55). An innocent infringer may face only an injunction and an account of profits.
You can sue in the district court where you reside or carry on business (section 62(2)).
Avoid threats you will not follow through on: section 60 allows a person threatened without basis to sue.

The honest answer usually needs someone to look at your actual disclosure, your timeline and the prior art. That is a conversation, not an article.