In the US, this would not even be close to rising to the level of stalking, in a legal sense. Even harassment could be a stretch (since obviously the legal use of harassment is different than casual conversational use). Stalking laws generally require the a “reasonable person” to fear for their safety and that the accused intended to cause them fear. Calling a business owner at inconvenient times is at best, meant to annoy. Even harassment typically involves things that have “no lawful purpose” and attempting to resolve a legitimate consumer complaint would likely be considered lawful.