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I can think of two possible issues at play here.
One issue is a difference in pronunciation between British RP ("Received Pronunciation", which is considered the standard pronunciation among all their regional varieties) and standard North American English (NA Eng). These are the pronunciations dictionaries give, rather than giving every regional ...
1
The pronunciations are usually distinct. For example, "doze" and "dose" are usually distinguished pretty easily.
A few caveats:
I live in the U.S. Northeast. Pronunciations in other regions might vary.
Some instances of "z" are not voiced. This is normal, for example, after "t" (spritz, putz, spitz, etc.). However, ...
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