Phone Verification Instagram

So a bunch of my instagram accounts need phone verification.
I phone verified them before already and got a bunch of sim cards for them.
I verified them manually with a phone, changing the sim card on the phone each time.

I have a spreadsheet for the phone numbers for each account. I allocated two accounts to each number.

However I am having trouble receiving the verification code from instagram. I currently need to re-verify the accounts. Sometimes the texts get sent through and sometimes they don't. Previously there were periods where one gets sent through and suddenly all of them are working. However other times nothing is being sent through.

Is this a problem with instagram or are my accounts/numbers flagged?
I called the mobile company and they assured me everything was working fine.

Thanks.

The problem is with IG at times. It does happens with everyone when working with masses. To wait for some time and trying again is the best option.