Do I need to file an annual return even if my company had no activity?

Yes. Under the Companies Act, Chapter 386 of the Laws of Malta, every registered company, dormant or active, is required to file an annual return with the Malta Business Registry (MBR) on each anniversary of its registration, along with the applicable fee, and this obligation is separate from filing financial statements or tax returns. Failure to file on time typically results in escalating penalties the longer the return remains outstanding, which is very likely what the letter you received relates to. You should file the outstanding annual returns as soon as possible to stop further penalties accruing and to avoid the more serious risk of the Registrar eventually striking the company off the register for non-compliance. If the company genuinely has no further use, it may be worth considering a formal voluntary dissolution instead of letting it remain dormant indefinitely, since that avoids ongoing annual filing obligations altogether. A licensed company service provider can help bring the filings up to date.