No logic...

So they send you your monthly invoice via e-mail in a format which isn't supported by my (very standard) laptop (why not just send it in a plain and simple pdf format that you know everyone will be able to open without any hassle?!). In order to view it online instead I thus went onto their website to hopefully get it from there. The site then requests you to first register an account - a process during which they then send you an OTP to the cellphone nr that you're registering the account for - in my case however - the same as hundreds of thousands of Cell C clients - I've only got a data contract with them, i.e. the simcard in use is in a router - and I also cannot even place the sim in my phone in order to easily receive the OTP as the size of the sim isn't the same as the size of my phone's sim! So why on earth, if you know that a very big/relative percentage of your clients are only data contract holders - and you have both your client's e-mail addresses as well as cellphone nrs - would you rather not just send the OTP's to (at least in the case of data-only-contract-holders) the e-mail addresses instead of via sms (or to simplify thing just both!) when it's very logic that a scenario of this kind will play out where I now can't just view my invoice, even after struggling a few mins with some as basic and unnecessary as this! Basics... Where's the logic?!