pentesting audit - CREST accreditation required

We're looking for a CREST-accredited penetration tester to assess our production SaaS platform. The test supports security due-diligence requests from our customers, so we need CVSS-scored findings with remediation guidance and a short attestation letter we can share with them. The platform has two parts, both hosted on AWS: a multi-tenant web application and REST API (PHP/Laravel, with role-based access and single sign-on), and a real-time voice-AI service (Python/FastAPI) that handles live phone calls via Twilio and Vonage and uses LLM and speech services. Our priorities are multi-tenant data isolation, authentication and authorization, the REST API, the telephony service, and resistance to LLM prompt injection. We expect standard OWASP methodology (WSTG/ASVS, API Top 10, LLM Top 10). This is a black-box engagement — no source code is provided. We'll supply test accounts across all roles and two tenant environments (under NDA) so authenticated and cross-tenant testing is possible. Deliverables are a full technical report, a shareable attestation summary, and a retest of remediated issues. In your proposal, please confirm your CREST accreditation, relevant experience (particularly telephony and LLM-based applications), estimated timeline, and cost.