Dyson Cordless Vacuum Cleaner Needs Full Inspection Not Partial Replacements

I called customer service about my Dyson cordless vacuum because the suction power has been going down during the warranty period. After looking at it over video call, they said the problem might be with the carpet brush and started the request for spare parts. But it's been two months and I still don't have the replacement part. Even though I called customer service several times, they told me that the delay was because the parts were coming from abroad and might be held up in customs. When I called customer service again, they told me that the problem might be with the filter and that I should wait for it to be fixed after I changed the filter. If the problem keeps happening, they said to check other parts. Now I'm asking that the vacuum be taken to technical service so that it can be looked at carefully. However, the people on the video calls tend to replace certain parts without directly addressing the problem, saying that this is what needs to be done and that they can't take the device into technical service right away. I don't like that Dyson uses a "trial and error" method by suggesting part replacements without first doing a full inspection. I insist on a full technical check of my vacuum so that the problem can be found and fixed correctly. Please solve my problem as soon as possible.