Yeah dot matrix printers can be quite a bit of trouble at times. Quite a lot I’ve used also don’t support all the ESC/POS commands sent using normal printer formatting tags.
However if it prints from Windows (i.e. try a test print from printers in Windows), then you should be able to print with HTML printer as long as you have the printer type in SambaPOS set as “HTML”.
Alternative, have a look at this other topic for an example printer template I did a while ago for a dot matrix printer using ESC/POS but specifying the actual escape codes to the printer using <XCT> (based on following from the command reference for the printer). Might work for you…