Cannot make additional purchases from SimpliSafe

I've been a subscriber for years and I've never been able to make additional purchases for products with SimpliSafe. I always have to buy from Best Buy or Amazon. For some reasons, my payments always get rejected. My autopay works perfectly though but my purchases always get rejected. I called SimpliSafe several times but it has been a waste of time. I called my banks, since I tried with different cards, and they all blame SimpliSafe merchant services. I get the approval from my banks every time, but the pending transactions end up dropping. SimpliSafe customer service refuses to accept that the issue is on their end. I don't blame them since they are not technicians. My last call today seemed to either have been disconnected or hung up. I've started looking for alternatives where I have the ability to upgrade at will. That is very disappointing.