Check which subtitles you are actually seeing
Open VLC’s Subtitle track menu and note the selected track. A media file can contain several languages, while an external file may have been added separately. Changing settings for an unused external file will not alter text coming from an embedded track.
Also check whether the words are burned into the video picture. If they remain when every subtitle track is disabled, they may be part of the image itself. That is a different case from a selectable subtitle stream, and ordinary subtitle font controls cannot edit the source video.
Distinguish rendered text from bitmap subtitles
VLC documents text-based subtitle controls and notes that image-based DVD/SVCD or VobSub subtitles do not respond to font changes in the same way. For VobSub, the documentation points to the index file rather than treating the companion data file as an ordinary text subtitle.
This does not mean the subtitle is defective. It means the available adjustment depends on its representation. Avoid downloading random replacement files merely to make a font preference work; use a legitimate alternative track supplied with the media when one is available.
Separate incorrect characters from poor sizing
Garbled letters in a text subtitle can be an encoding issue, while tiny but correct text is a presentation issue. VLC’s documentation includes character encoding when loading an external subtitle file. Match the setting to the actual file instead of changing the programme’s audio language.
For font changes, restart the stream where required by VLC’s documented workflow, then return to the same line for comparison. A new scene with different text length is a less useful test. Check the result at the normal viewing distance and without a menu covering the bottom of the frame.
Keep a useful example for support
Record whether the subtitle is embedded, external text, an image track or burned into the picture. Include the VLC version and the behaviour after disabling the selected track. Those details explain much more than a screenshot labelled subtitles broken.
Do not distribute an entire copyrighted media file just to demonstrate a font problem. A short description, the format and a redacted settings image may be enough for the publisher to guide the next step. If the actual problem is timing, investigate offset separately from font and encoding.