Advice on improving campaign performance

My partner and I started an email outreach agency and are trying to get a client through cold emails. In the first 2 weeks using Lemlist, our campaign metrics were looking like this:
- 50 emails sent
- 46% open rate
- 10% reply rate (16% at a certain point)
- 1 booked meeting

But then right after that, our campaigns tanked to the bottom when we moved to Smartlead. The same script that got us that result didn't work with new leads, so we A/B tested a new script, but still no improvement. We are still A/B testing new scripts and scraping new leads using apollo.io and clay.com (all free versions)

We assume it's the script since our reply rate is almost at zero, but feedback and advice are appreciated