Can I ask what things have you tried?
How many visitors were you getting when you were ranked 25 and how many are you getting now?
You want to be aiming to be on the first page (spots 1 - 3 ideally) going from 25 - 70 will make hardly any difference in actual visitors imo.
Do you know when this drop occured?
If the product is becoming increasingly popular it could be a fact that other sites are moving up due to relevance and you down and you need to adjust your approach a little.
Another thing is alot of your competitors have the words "bike" or "electric" in their domain name and this helps too, you don't.
Anchor Text for you is REALLY important so every link you get from now on make sure it says Electric Bikes or Buy Electric Bikes (as that what you want people to do buy your bikes) You will rank for your brand name with any issue so try to avoid any further links with your brand name.
I would even go as far as changing the tab that says "bike" to "Electric Bikes" also.
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As a side note:
When you get visitors to your site I feel you will have a issue with converting as many as you "could" because your site isn't very friendly it shouldn't be on black it makes it very hard to read but you may not deal with that nor want to talk about that yet....