Did you take it apart? Any firearm that has to be returned or taken to a certified armorer is going to be a hassle, and because there are limited certified HK Armorers in Canada, it would be almost certainly a time consuming task. ( as far as I know, there are only 4 certified for Canada (civilian), some LE and I would assume some military.
Try the HKpro website, they have an HK facts page, it has troubleshooting sections that may have a solutiion.
Do all you mags get hung up, or only one? Is the magwell clean? Are the mags clean? IF the fit seems to tight, try a 1000-1200 grit sand paper, and lightly polish the outside of the mags. Check for any loose pieces of plastic inside the mag well that may be catching the mags. Some HK mag releases are stiff when new, and may even require a small amount of oil.