Wow, I’m really sorry your husband’s having such a rough go of this! And I’m sure it’s really discouraging not to get his usual comprehensive care from the clinic. How long ago was he injured?

Does he have any of the following symptoms?
Drainage from the wound such as pus
Redness or warmth around the wound, particularly if it’s spreading
Bad odor
Increasing pain
Darkening skin at the edges
Fever

You mentioned different wound care treatments that he’s tried. Has he reported to the Wound clinic that there is still some peripheral tissue damage happening? Were they the ones recommending the change in dressing? In my opinion, they may need to get more aggressive if this has been going on for some time.
Does your husband have any underlying conditions such a diabetes which could be slowing his healing?