If they deceived you into granting permission to remotely access and control your Mac under false premises, it is not unreasonable to assume that they are criminals who now have identical access and control privileges over it as you. You need no more justification to support that conclusion than the company's initial assertion "iOS was about to crash" which is of course absurd for a variety of technical reasons.
Your actions at this point can range from doing nothing at all, to erasing the Mac and reconfiguring it. Separately, it would be prudent to assume the intruder has gained sufficient information from it to effectively commit identity theft. Computer tampering and identity theft are legal matters that go well beyond the scope of this support site, and for which you should seek appropriate legal counsel. Therefore I can only offer technical guidance regarding your Mac itself, which may be considered evidence in a criminal proceeding that only you can decide to take upon receiving that counsel.
At a minimum it should be immediately disconnected from the Internet (unplug its Ethernet cable and turn Wi-Fi "off") after which you can decide whether to preserve it in its present condition as evidence, or its contents completely erased, permanently removing that evidence. Decide how you want to proceed and write back.