I really wouldn’t quibble over 10 minutes on one occasion - there will be a visit at some point when he needs an extra few minutes and you'd want him to be given it. If it's happening regularly, then it does need bringing up.
Instead, you need to report tasks not being done properly, like being left in his coat, and explain why it's important.
Bear in mind that genuine misunderstandings occur - the carer may have asked him and he'd said he wanted his coat on, without realising how he would interpret this later.
Regarding the fill-ins, we've noticed they started during the week, but only received a letter today explaining the measures being taken due to cv19. You need to cut the agency some slack about deploying different staff at the moment. If the regular staff are unwell or self-isolating, you wouldn’t want them there anyway.
The managers who would normally have called you are probably absent or out doing care visits themselves, so it's probably on you to let them know in advance if you'd prefer to cover the visits yourself if the regular carers aren't available.
None of that excuses taking a client’s belongings though.